diff --git a/core/client/db/src/lib.rs b/core/client/db/src/lib.rs
index 60196e4a322bb..93a5352fd7b51 100644
--- a/core/client/db/src/lib.rs
+++ b/core/client/db/src/lib.rs
@@ -64,7 +64,7 @@ use hash_db::Hasher;
 use kvdb::{KeyValueDB, DBTransaction};
 use trie::MemoryDB;
 use parking_lot::RwLock;
-use primitives::{H256, AuthorityId, Blake2Hasher, ChangesTrieConfiguration};
+use primitives::{H256, AuthorityId, Blake2Hasher, ChangesTrieConfiguration, convert_hash};
 use primitives::storage::well_known_keys;
 use runtime_primitives::{generic::BlockId, Justification, StorageMap, ChildrenStorageMap};
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, As, NumberFor, Zero, Digest, DigestItem};
@@ -145,7 +145,7 @@ impl<'a> state_db::MetaDb for StateMetaDb<'a> {
 /// Block database
 pub struct BlockchainDb<Block: BlockT> {
 	db: Arc<KeyValueDB>,
-	meta: RwLock<Meta<NumberFor<Block>, Block::Hash>>,
+	meta: Arc<RwLock<Meta<NumberFor<Block>, Block::Hash>>>,
 	leaves: RwLock<LeafSet<Block::Hash, NumberFor<Block>>>,
 }
 
@@ -156,7 +156,7 @@ impl<Block: BlockT> BlockchainDb<Block> {
 		Ok(BlockchainDb {
 			db,
 			leaves: RwLock::new(leaves),
-			meta: RwLock::new(meta),
+			meta: Arc::new(RwLock::new(meta)),
 		})
 	}
 
@@ -387,6 +387,7 @@ impl state_machine::Storage<Blake2Hasher> for DbGenesisStorage {
 
 pub struct DbChangesTrieStorage<Block: BlockT> {
 	db: Arc<KeyValueDB>,
+	meta: Arc<RwLock<Meta<NumberFor<Block>, Block::Hash>>>,
 	min_blocks_to_keep: Option<u64>,
 	_phantom: ::std::marker::PhantomData<Block>,
 }
@@ -400,7 +401,7 @@ impl<Block: BlockT> DbChangesTrieStorage<Block> {
 	}
 
 	/// Prune obsolete changes tries.
-	pub fn prune(&self, config: Option<ChangesTrieConfiguration>, tx: &mut DBTransaction, block: NumberFor<Block>) {
+	pub fn prune(&self, config: Option<ChangesTrieConfiguration>, tx: &mut DBTransaction, block_hash: Block::Hash, block_num: NumberFor<Block>) {
 		// never prune on archive nodes
 		let min_blocks_to_keep = match self.min_blocks_to_keep {
 			Some(min_blocks_to_keep) => min_blocks_to_keep,
@@ -418,23 +419,54 @@ impl<Block: BlockT> DbChangesTrieStorage<Block> {
 			&config,
 			&*self,
 			min_blocks_to_keep,
-			block.as_(),
+			&state_machine::ChangesTrieAnchorBlockId {
+				hash: convert_hash(&block_hash),
+				number: block_num.as_(),
+			},
 			|node| tx.delete(columns::CHANGES_TRIE, node.as_ref()));
 	}
 }
 
 impl<Block: BlockT> state_machine::ChangesTrieRootsStorage<Blake2Hasher> for DbChangesTrieStorage<Block> {
-	fn root(&self, block: u64) -> Result<Option<H256>, String> {
-		Ok(read_db::<Block>(&*self.db, columns::HASH_LOOKUP, columns::HEADER, BlockId::Number(As::sa(block)))
-			.map_err(|err| format!("{}", err))
-			.and_then(|header| match header {
-				Some(header) => Block::Header::decode(&mut &header[..])
-					.ok_or_else(|| format!("Failed to parse header of block {}", block))
-					.map(Some),
-				None => Ok(None)
-			})?
-			.and_then(|header| header.digest().log(DigestItem::as_changes_trie_root)
-				.map(|root| H256::from_slice(root.as_ref()))))
+	fn root(&self, anchor: &state_machine::ChangesTrieAnchorBlockId<H256>, block: u64) -> Result<Option<H256>, String> {
+		// check API requirement
+		assert!(block <= anchor.number, "API requirement");
+
+		// we need to get hash of the block to resolve changes trie root
+		let block_id = if block <= self.meta.read().finalized_number.as_() {
+			// if block is finalized, we could just read canonical hash
+			BlockId::Number(As::sa(block))
+		} else {
+			// the block is not finalized
+			let mut current_num = anchor.number;
+			let mut current_hash: Block::Hash = convert_hash(&anchor.hash);
+			let maybe_anchor_header: Block::Header = ::utils::require_header::<Block>(
+				&*self.db, columns::HASH_LOOKUP, columns::HEADER, BlockId::Number(As::sa(current_num))
+			).map_err(|e| e.to_string())?;
+			if maybe_anchor_header.hash() == current_hash {
+				// if anchor is canonicalized, then the block is also canonicalized
+				BlockId::Number(As::sa(block))
+			} else {
+				// else (block is not finalized + anchor is not canonicalized):
+				// => we should find the required block hash by traversing
+				// back from the anchor to the block with given number
+				while current_num != block {
+					let current_header: Block::Header = ::utils::require_header::<Block>(
+						&*self.db, columns::HASH_LOOKUP, columns::HEADER, BlockId::Hash(current_hash)
+					).map_err(|e| e.to_string())?;
+
+					current_hash = *current_header.parent_hash();
+					current_num = current_num - 1;
+				}
+
+				BlockId::Hash(current_hash)
+			}
+		};
+
+		Ok(::utils::require_header::<Block>(&*self.db, columns::HASH_LOOKUP, columns::HEADER, block_id)
+			.map_err(|e| e.to_string())?
+			.digest().log(DigestItem::as_changes_trie_root)
+			.map(|root| H256::from_slice(root.as_ref())))
 	}
 }
 
@@ -480,6 +512,7 @@ impl<Block: BlockT> Backend<Block> {
 	fn from_kvdb(db: Arc<KeyValueDB>, pruning: PruningMode, canonicalization_delay: u64) -> Result<Self, client::error::Error> {
 		let is_archive_pruning = pruning.is_archive();
 		let blockchain = BlockchainDb::new(db.clone())?;
+		let meta = blockchain.meta.clone();
 		let map_e = |e: state_db::Error<io::Error>| ::client::error::Error::from(format!("State database error: {:?}", e));
 		let state_db: StateDb<Block::Hash, H256> = StateDb::new(pruning, &StateMetaDb(&*db)).map_err(map_e)?;
 		let storage_db = StorageDb {
@@ -488,6 +521,7 @@ impl<Block: BlockT> Backend<Block> {
 		};
 		let changes_tries_storage = DbChangesTrieStorage {
 			db,
+			meta,
 			min_blocks_to_keep: if is_archive_pruning { None } else { Some(MIN_BLOCKS_TO_KEEP_CHANGES_TRIES_FOR) },
 			_phantom: Default::default(),
 		};
@@ -567,7 +601,7 @@ impl<Block: BlockT> Backend<Block> {
 			let changes_trie_config: Option<ChangesTrieConfiguration> = self.state_at(BlockId::Hash(parent_hash))?
 				.storage(well_known_keys::CHANGES_TRIE_CONFIG)?
 				.and_then(|v| Decode::decode(&mut &*v));
-			self.changes_tries_storage.prune(changes_trie_config, transaction, f_num);
+			self.changes_tries_storage.prune(changes_trie_config, transaction, f_hash, f_num);
 		}
 
 		Ok(())
@@ -1191,10 +1225,13 @@ mod tests {
 	#[test]
 	fn changes_trie_storage_works() {
 		let backend = Backend::<Block>::new_test(1000, 100);
+		backend.changes_tries_storage.meta.write().finalized_number = 1000;
+
 
 		let check_changes = |backend: &Backend<Block>, block: u64, changes: Vec<(Vec<u8>, Vec<u8>)>| {
 			let (changes_root, mut changes_trie_update) = prepare_changes(changes);
-			assert_eq!(backend.changes_tries_storage.root(block), Ok(Some(changes_root)));
+			let anchor = state_machine::ChangesTrieAnchorBlockId { hash: Default::default(), number: block };
+			assert_eq!(backend.changes_tries_storage.root(&anchor, block), Ok(Some(changes_root)));
 
 			for (key, (val, _)) in changes_trie_update.drain() {
 				assert_eq!(backend.changes_trie_storage().unwrap().get(&key), Ok(Some(val)));
@@ -1218,9 +1255,66 @@ mod tests {
 		check_changes(&backend, 2, changes2);
 	}
 
+	#[test]
+	fn changes_trie_storage_works_with_forks() {
+		let backend = Backend::<Block>::new_test(1000, 100);
+
+		let changes0 = vec![(b"k0".to_vec(), b"v0".to_vec())];
+		let changes1 = vec![(b"k1".to_vec(), b"v1".to_vec())];
+		let changes2 = vec![(b"k2".to_vec(), b"v2".to_vec())];
+		let block0 = insert_header(&backend, 0, Default::default(), changes0.clone(), Default::default());
+		let block1 = insert_header(&backend, 1, block0, changes1.clone(), Default::default());
+		let block2 = insert_header(&backend, 2, block1, changes2.clone(), Default::default());
+
+		let changes2_1_0 = vec![(b"k3".to_vec(), b"v3".to_vec())];
+		let changes2_1_1 = vec![(b"k4".to_vec(), b"v4".to_vec())];
+		let block2_1_0 = insert_header(&backend, 3, block2, changes2_1_0.clone(), Default::default());
+		let block2_1_1 = insert_header(&backend, 4, block2_1_0, changes2_1_1.clone(), Default::default());
+
+		let changes2_2_0 = vec![(b"k5".to_vec(), b"v5".to_vec())];
+		let changes2_2_1 = vec![(b"k6".to_vec(), b"v6".to_vec())];
+		let block2_2_0 = insert_header(&backend, 3, block2, changes2_2_0.clone(), Default::default());
+		let block2_2_1 = insert_header(&backend, 4, block2_2_0, changes2_2_1.clone(), Default::default());
+
+		// finalize block1
+		backend.changes_tries_storage.meta.write().finalized_number = 1;
+
+		// branch1: when asking for finalized block hash
+		let (changes1_root, _) = prepare_changes(changes1);
+		let anchor = state_machine::ChangesTrieAnchorBlockId { hash: block2_1_1, number: 4 };
+		assert_eq!(backend.changes_tries_storage.root(&anchor, 1), Ok(Some(changes1_root)));
+
+		// branch2: when asking for finalized block hash
+		let anchor = state_machine::ChangesTrieAnchorBlockId { hash: block2_2_1, number: 4 };
+		assert_eq!(backend.changes_tries_storage.root(&anchor, 1), Ok(Some(changes1_root)));
+
+		// branch1: when asking for non-finalized block hash (search by traversal)
+		let (changes2_1_0_root, _) = prepare_changes(changes2_1_0);
+		let anchor = state_machine::ChangesTrieAnchorBlockId { hash: block2_1_1, number: 4 };
+		assert_eq!(backend.changes_tries_storage.root(&anchor, 3), Ok(Some(changes2_1_0_root)));
+
+		// branch2: when asking for non-finalized block hash (search using canonicalized hint)
+		let (changes2_2_0_root, _) = prepare_changes(changes2_2_0);
+		let anchor = state_machine::ChangesTrieAnchorBlockId { hash: block2_2_1, number: 4 };
+		assert_eq!(backend.changes_tries_storage.root(&anchor, 3), Ok(Some(changes2_2_0_root)));
+
+		// finalize first block of branch2 (block2_2_0)
+		backend.changes_tries_storage.meta.write().finalized_number = 3;
+
+		// branch2: when asking for finalized block of this branch
+		assert_eq!(backend.changes_tries_storage.root(&anchor, 3), Ok(Some(changes2_2_0_root)));
+
+		// branch1: when asking for finalized block of other branch
+		// => result is incorrect (returned for the block of branch1), but this is expected,
+		// because the other fork is abandoned (forked before finalized header)
+		let anchor = state_machine::ChangesTrieAnchorBlockId { hash: block2_1_1, number: 4 };
+		assert_eq!(backend.changes_tries_storage.root(&anchor, 3), Ok(Some(changes2_2_0_root)));
+	}
+
 	#[test]
 	fn changes_tries_are_pruned_on_finalization() {
 		let mut backend = Backend::<Block>::new_test(1000, 100);
+		backend.changes_tries_storage.meta.write().finalized_number = 1000;
 		backend.changes_tries_storage.min_blocks_to_keep = Some(8);
 		let config = ChangesTrieConfiguration {
 			digest_interval: 2,
@@ -1243,26 +1337,27 @@ mod tests {
 		let _ = insert_header(&backend, 12, block11, vec![(b"key_at_12".to_vec(), b"val_at_12".to_vec())], Default::default());
 
 		// check that roots of all tries are in the columns::CHANGES_TRIE
+		let anchor = state_machine::ChangesTrieAnchorBlockId { hash: Default::default(), number: 100 };
 		fn read_changes_trie_root(backend: &Backend<Block>, num: u64) -> H256 {
 			backend.blockchain().header(BlockId::Number(num)).unwrap().unwrap().digest().logs().iter()
 				.find(|i| i.as_changes_trie_root().is_some()).unwrap().as_changes_trie_root().unwrap().clone()
 		}
-		let root1 = read_changes_trie_root(&backend, 1); assert_eq!(backend.changes_tries_storage.root(1).unwrap(), Some(root1));
-		let root2 = read_changes_trie_root(&backend, 2); assert_eq!(backend.changes_tries_storage.root(2).unwrap(), Some(root2));
-		let root3 = read_changes_trie_root(&backend, 3); assert_eq!(backend.changes_tries_storage.root(3).unwrap(), Some(root3));
-		let root4 = read_changes_trie_root(&backend, 4); assert_eq!(backend.changes_tries_storage.root(4).unwrap(), Some(root4));
-		let root5 = read_changes_trie_root(&backend, 5); assert_eq!(backend.changes_tries_storage.root(5).unwrap(), Some(root5));
-		let root6 = read_changes_trie_root(&backend, 6); assert_eq!(backend.changes_tries_storage.root(6).unwrap(), Some(root6));
-		let root7 = read_changes_trie_root(&backend, 7); assert_eq!(backend.changes_tries_storage.root(7).unwrap(), Some(root7));
-		let root8 = read_changes_trie_root(&backend, 8); assert_eq!(backend.changes_tries_storage.root(8).unwrap(), Some(root8));
-		let root9 = read_changes_trie_root(&backend, 9); assert_eq!(backend.changes_tries_storage.root(9).unwrap(), Some(root9));
-		let root10 = read_changes_trie_root(&backend, 10); assert_eq!(backend.changes_tries_storage.root(10).unwrap(), Some(root10));
-		let root11 = read_changes_trie_root(&backend, 11); assert_eq!(backend.changes_tries_storage.root(11).unwrap(), Some(root11));
-		let root12 = read_changes_trie_root(&backend, 12); assert_eq!(backend.changes_tries_storage.root(12).unwrap(), Some(root12));
+		let root1 = read_changes_trie_root(&backend, 1); assert_eq!(backend.changes_tries_storage.root(&anchor, 1).unwrap(), Some(root1));
+		let root2 = read_changes_trie_root(&backend, 2); assert_eq!(backend.changes_tries_storage.root(&anchor, 2).unwrap(), Some(root2));
+		let root3 = read_changes_trie_root(&backend, 3); assert_eq!(backend.changes_tries_storage.root(&anchor, 3).unwrap(), Some(root3));
+		let root4 = read_changes_trie_root(&backend, 4); assert_eq!(backend.changes_tries_storage.root(&anchor, 4).unwrap(), Some(root4));
+		let root5 = read_changes_trie_root(&backend, 5); assert_eq!(backend.changes_tries_storage.root(&anchor, 5).unwrap(), Some(root5));
+		let root6 = read_changes_trie_root(&backend, 6); assert_eq!(backend.changes_tries_storage.root(&anchor, 6).unwrap(), Some(root6));
+		let root7 = read_changes_trie_root(&backend, 7); assert_eq!(backend.changes_tries_storage.root(&anchor, 7).unwrap(), Some(root7));
+		let root8 = read_changes_trie_root(&backend, 8); assert_eq!(backend.changes_tries_storage.root(&anchor, 8).unwrap(), Some(root8));
+		let root9 = read_changes_trie_root(&backend, 9); assert_eq!(backend.changes_tries_storage.root(&anchor, 9).unwrap(), Some(root9));
+		let root10 = read_changes_trie_root(&backend, 10); assert_eq!(backend.changes_tries_storage.root(&anchor, 10).unwrap(), Some(root10));
+		let root11 = read_changes_trie_root(&backend, 11); assert_eq!(backend.changes_tries_storage.root(&anchor, 11).unwrap(), Some(root11));
+		let root12 = read_changes_trie_root(&backend, 12); assert_eq!(backend.changes_tries_storage.root(&anchor, 12).unwrap(), Some(root12));
 
 		// now simulate finalization of block#12, causing prune of tries at #1..#4
 		let mut tx = DBTransaction::new();
-		backend.changes_tries_storage.prune(Some(config.clone()), &mut tx, 12);
+		backend.changes_tries_storage.prune(Some(config.clone()), &mut tx, Default::default(), 12);
 		backend.storage.db.write(tx).unwrap();
 		assert!(backend.changes_tries_storage.get(&root1).unwrap().is_none());
 		assert!(backend.changes_tries_storage.get(&root2).unwrap().is_none());
@@ -1275,7 +1370,7 @@ mod tests {
 
 		// now simulate finalization of block#16, causing prune of tries at #5..#8
 		let mut tx = DBTransaction::new();
-		backend.changes_tries_storage.prune(Some(config.clone()), &mut tx, 16);
+		backend.changes_tries_storage.prune(Some(config.clone()), &mut tx, Default::default(), 16);
 		backend.storage.db.write(tx).unwrap();
 		assert!(backend.changes_tries_storage.get(&root5).unwrap().is_none());
 		assert!(backend.changes_tries_storage.get(&root6).unwrap().is_none());
@@ -1286,7 +1381,7 @@ mod tests {
 		// => no changes tries are pruned, because we never prune in archive mode
 		backend.changes_tries_storage.min_blocks_to_keep = None;
 		let mut tx = DBTransaction::new();
-		backend.changes_tries_storage.prune(Some(config), &mut tx, 20);
+		backend.changes_tries_storage.prune(Some(config), &mut tx, Default::default(), 20);
 		backend.storage.db.write(tx).unwrap();
 		assert!(backend.changes_tries_storage.get(&root9).unwrap().is_some());
 		assert!(backend.changes_tries_storage.get(&root10).unwrap().is_some());
diff --git a/core/client/db/src/utils.rs b/core/client/db/src/utils.rs
index f7b81845e8e7c..5caebd7e72ec5 100644
--- a/core/client/db/src/utils.rs
+++ b/core/client/db/src/utils.rs
@@ -187,6 +187,17 @@ pub fn read_header<Block: BlockT>(
 	}
 }
 
+/// Required header from the database.
+pub fn require_header<Block: BlockT>(
+	db: &KeyValueDB,
+	col_index: Option<u32>,
+	col: Option<u32>,
+	id: BlockId<Block>,
+) -> client::error::Result<Block::Header> {
+	read_header(db, col_index, col, id)
+		.and_then(|header| header.ok_or_else(|| client::error::ErrorKind::UnknownBlock(format!("{}", id)).into()))
+}
+
 /// Read meta from the database.
 pub fn read_meta<Block>(db: &KeyValueDB, col_meta: Option<u32>, col_header: Option<u32>) -> Result<
 	Meta<<<Block as BlockT>::Header as HeaderT>::Number, Block::Hash>,
diff --git a/core/client/src/cht.rs b/core/client/src/cht.rs
index fd8e07c3dd4bc..39e1aaa95bd25 100644
--- a/core/client/src/cht.rs
+++ b/core/client/src/cht.rs
@@ -27,7 +27,7 @@ use hash_db;
 use heapsize::HeapSizeOf;
 use trie;
 
-use primitives::H256;
+use primitives::{H256, convert_hash};
 use runtime_primitives::traits::{As, Header as HeaderT, SimpleArithmetic, One};
 use state_machine::backend::InMemory as InMemoryState;
 use state_machine::{prove_read, read_proof_check};
@@ -113,8 +113,7 @@ pub fn check_proof<Header, Hasher>(
 		Hasher: hash_db::Hasher,
 		Hasher::Out: Ord + HeapSizeOf,
 {
-	let mut root: Hasher::Out = Default::default();
-	root.as_mut().copy_from_slice(local_root.as_ref());
+	let root: Hasher::Out = convert_hash(&local_root);
 	let local_cht_key = encode_cht_key(local_number);
 	let local_cht_value = read_proof_check::<Hasher>(root, remote_proof,
 		&local_cht_key).map_err(|e| ClientError::from(e))?;
diff --git a/core/client/src/client.rs b/core/client/src/client.rs
index 1279bc486a314..f1d1549185cd1 100644
--- a/core/client/src/client.rs
+++ b/core/client/src/client.rs
@@ -30,14 +30,14 @@ use consensus::{ImportBlock, ImportResult, BlockOrigin};
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, Zero, As, NumberFor, CurrentHeight, BlockNumberToHash};
 use runtime_primitives::{ApplyResult, BuildStorage};
 use runtime_api as api;
-use primitives::{Blake2Hasher, H256, ChangesTrieConfiguration};
+use primitives::{Blake2Hasher, H256, ChangesTrieConfiguration, convert_hash};
 use primitives::storage::{StorageKey, StorageData};
 use primitives::storage::well_known_keys;
 use codec::{Encode, Decode};
 use state_machine::{
 	Backend as StateBackend, CodeExecutor,
-	ExecutionStrategy, ExecutionManager, prove_read,
-	key_changes, key_changes_proof, OverlayedChanges
+	ExecutionStrategy, ExecutionManager, ChangesTrieAnchorBlockId,
+	prove_read, key_changes, key_changes_proof, OverlayedChanges
 };
 
 use backend::{self, BlockImportOperation};
@@ -355,7 +355,10 @@ impl<B, E, Block> Client<B, E, Block> where
 			config,
 			storage,
 			self.require_block_number_from_id(&BlockId::Hash(first))?.as_(),
-			self.require_block_number_from_id(&BlockId::Hash(last))?.as_(),
+			&ChangesTrieAnchorBlockId {
+				hash: convert_hash(&last),
+				number: self.require_block_number_from_id(&BlockId::Hash(last))?.as_(),
+			},
 			self.backend.blockchain().info()?.best_number.as_(),
 			key)
 		.map_err(|err| error::ErrorKind::ChangesTrieAccessFailed(err).into())
@@ -388,7 +391,10 @@ impl<B, E, Block> Client<B, E, Block> where
 			config,
 			storage,
 			self.require_block_number_from_id(&BlockId::Hash(first))?.as_(),
-			self.require_block_number_from_id(&BlockId::Hash(last))?.as_(),
+			&ChangesTrieAnchorBlockId {
+				hash: convert_hash(&last),
+				number: self.require_block_number_from_id(&BlockId::Hash(last))?.as_(),
+			},
 			max_number.as_(),
 			key)
 		.map_err(|err| error::ErrorKind::ChangesTrieAccessFailed(err).into())
diff --git a/core/client/src/light/call_executor.rs b/core/client/src/light/call_executor.rs
index d52883db64f01..732b783b73adc 100644
--- a/core/client/src/light/call_executor.rs
+++ b/core/client/src/light/call_executor.rs
@@ -21,6 +21,7 @@ use std::marker::PhantomData;
 use std::sync::Arc;
 use futures::{IntoFuture, Future};
 
+use primitives::convert_hash;
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT};
 use state_machine::{Backend as StateBackend, CodeExecutor, OverlayedChanges,
@@ -136,8 +137,7 @@ pub fn check_execution_proof<Header, E, H>(
 
 {
 	let local_state_root = request.header.state_root();
-	let mut root: H::Out = Default::default();
-	root.as_mut().copy_from_slice(local_state_root.as_ref());
+	let root: H::Out = convert_hash(&local_state_root);
 
 	let mut changes = OverlayedChanges::default();
 	let local_result = execution_proof_check::<H, _>(
diff --git a/core/client/src/light/fetcher.rs b/core/client/src/light/fetcher.rs
index 95e02b91f9f65..b75b74a0a976e 100644
--- a/core/client/src/light/fetcher.rs
+++ b/core/client/src/light/fetcher.rs
@@ -21,10 +21,10 @@ use futures::IntoFuture;
 
 use hash_db::Hasher;
 use heapsize::HeapSizeOf;
-use primitives::ChangesTrieConfiguration;
+use primitives::{ChangesTrieConfiguration, convert_hash};
 use runtime_primitives::traits::{As, Block as BlockT, Header as HeaderT, NumberFor};
-use state_machine::{CodeExecutor, ChangesTrieRootsStorage, read_proof_check,
-	key_changes_proof_check};
+use state_machine::{CodeExecutor, ChangesTrieRootsStorage, ChangesTrieAnchorBlockId,
+	read_proof_check, key_changes_proof_check};
 
 use call_executor::CallResult;
 use cht;
@@ -192,9 +192,8 @@ impl<E, Block, H> FetchChecker<Block> for LightDataChecker<E, H>
 		request: &RemoteReadRequest<Block::Header>,
 		remote_proof: Vec<Vec<u8>>
 	) -> ClientResult<Option<Vec<u8>>> {
-		let mut root: H::Out = Default::default();
-		root.as_mut().copy_from_slice(request.header.state_root().as_ref());
-		read_proof_check::<H>(root, remote_proof, &request.key).map_err(Into::into)
+		read_proof_check::<H>(convert_hash(request.header.state_root()), remote_proof, &request.key)
+			.map_err(Into::into)
 	}
 
 	fn check_execution_proof(
@@ -229,7 +228,10 @@ impl<E, Block, H> FetchChecker<Block> for LightDataChecker<E, H>
 			},
 			remote_proof,
 			first_number,
-			request.last_block.0.as_(),
+			&ChangesTrieAnchorBlockId {
+				hash: convert_hash(&request.last_block.1),
+				number: request.last_block.0.as_(),
+			},
 			remote_max.as_(),
 			&request.key)
 		.map(|pairs| pairs.into_iter().map(|(b, x)| (As::sa(b), x)).collect())
@@ -248,15 +250,12 @@ impl<'a, H, Hash> ChangesTrieRootsStorage<H> for RootsStorage<'a, Hash>
 		H: Hasher,
 		Hash: 'a + Send + Sync + Clone + AsRef<[u8]>,
 {
-	fn root(&self, block: u64) -> Result<Option<H::Out>, String> {
+	fn root(&self, _anchor: &ChangesTrieAnchorBlockId<H::Out>, block: u64) -> Result<Option<H::Out>, String> {
+		// we can't ask for roots from parallel forks here => ignore anchor
 		Ok(block.checked_sub(self.first)
 			.and_then(|index| self.roots.get(index as usize))
 			.cloned()
-			.map(|root| {
-				let mut hasher_root: H::Out = Default::default();
-				hasher_root.as_mut().copy_from_slice(root.as_ref());
-				hasher_root
-			}))
+			.map(|root| convert_hash(&root)))
 	}
 }
 
diff --git a/core/executor/src/wasm_executor.rs b/core/executor/src/wasm_executor.rs
index 90d6db600151a..7480b6195014a 100644
--- a/core/executor/src/wasm_executor.rs
+++ b/core/executor/src/wasm_executor.rs
@@ -29,7 +29,7 @@ use wasm_utils::UserError;
 use primitives::{blake2_256, twox_128, twox_256, ed25519};
 use primitives::hexdisplay::HexDisplay;
 use primitives::sandbox as sandbox_primitives;
-use primitives::Blake2Hasher;
+use primitives::{H256, Blake2Hasher};
 use trie::ordered_trie_root;
 use sandbox;
 
@@ -412,8 +412,15 @@ impl_function_executor!(this: FunctionExecutor<'e, E>,
 			Ok(0)
 		}
 	},
-	ext_storage_changes_root(block: u64, result: *mut u8) -> u32 => {
-		let r = this.ext.storage_changes_root(block);
+	ext_storage_changes_root(parent_hash_data: *const u8, parent_hash_len: u32, parent_number: u64, result: *mut u8) -> u32 => {
+		let mut parent_hash = H256::default();
+		if parent_hash_len != parent_hash.as_ref().len() as u32 {
+			return Err(UserError("Invalid parent_hash_len in ext_storage_changes_root").into());
+		}
+		let raw_parent_hash = this.memory.get(parent_hash_data, parent_hash_len as usize)
+			.map_err(|_| UserError("Invalid attempt to get parent_hash in ext_storage_changes_root"))?;
+		parent_hash.as_mut().copy_from_slice(&raw_parent_hash[..]);
+		let r = this.ext.storage_changes_root(parent_hash, parent_number);
 		if let Some(ref r) = r {
 			this.memory.set(result, &r[..]).map_err(|_| UserError("Invalid attempt to set memory in ext_storage_changes_root"))?;
 		}
diff --git a/core/primitives/src/hash.rs b/core/primitives/src/hash.rs
index 5733a738c9b93..8d04df26844db 100644
--- a/core/primitives/src/hash.rs
+++ b/core/primitives/src/hash.rs
@@ -76,6 +76,16 @@ impl_rest!(H160, 20);
 impl_rest!(H256, 32);
 impl_rest!(H512, 64);
 
+/// Hash conversion. Used to convert between unbound associated hash types in traits,
+/// implemented by the same hash type.
+/// Panics if used to convert between different hash types.
+pub fn convert_hash<H1: Default + AsMut<[u8]>, H2: AsRef<[u8]>>(src: &H2) -> H1 {
+	let mut dest = H1::default();
+	assert_eq!(dest.as_mut().len(), src.as_ref().len());
+	dest.as_mut().copy_from_slice(src.as_ref());
+	dest
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
diff --git a/core/primitives/src/lib.rs b/core/primitives/src/lib.rs
index c5ddcb130dbc8..20f044a872725 100644
--- a/core/primitives/src/lib.rs
+++ b/core/primitives/src/lib.rs
@@ -107,7 +107,7 @@ mod changes_trie;
 #[cfg(test)]
 mod tests;
 
-pub use self::hash::{H160, H256, H512};
+pub use self::hash::{H160, H256, H512, convert_hash};
 pub use self::uint::U256;
 pub use authority_id::AuthorityId;
 pub use changes_trie::ChangesTrieConfiguration;
diff --git a/core/sr-io/with_std.rs b/core/sr-io/with_std.rs
index 72fa107469853..a608a632fe136 100644
--- a/core/sr-io/with_std.rs
+++ b/core/sr-io/with_std.rs
@@ -157,9 +157,9 @@ pub fn child_storage_root(storage_key: &[u8]) -> Option<Vec<u8>> {
 }
 
 /// "Commit" all existing operations and get the resultant storage change root.
-pub fn storage_changes_root(block: u64) -> Option<H256> {
+pub fn storage_changes_root(parent_hash: [u8; 32], parent_num: u64) -> Option<H256> {
 	ext::with(|ext|
-		ext.storage_changes_root(block)
+		ext.storage_changes_root(parent_hash.into(), parent_num)
 	).unwrap_or(None)
 }
 
diff --git a/core/sr-io/without_std.rs b/core/sr-io/without_std.rs
index 5b892ecffe6bb..d0f112b76e8bf 100644
--- a/core/sr-io/without_std.rs
+++ b/core/sr-io/without_std.rs
@@ -72,7 +72,7 @@ extern "C" {
 	fn ext_get_child_storage_into(storage_key_data: *const u8, storage_key_len: u32, key_data: *const u8, key_len: u32, value_data: *mut u8, value_len: u32, value_offset: u32) -> u32;
 	fn ext_storage_root(result: *mut u8);
 	fn ext_child_storage_root(storage_key_data: *const u8, storage_key_len: u32, written_out: *mut u32) -> *mut u8;
-	fn ext_storage_changes_root(block: u64, result: *mut u8) -> u32;
+	fn ext_storage_changes_root(parent_hash_data: *const u8, parent_hash_len: u32, parent_num: u64, result: *mut u8) -> u32;
 	fn ext_blake2_256_enumerated_trie_root(values_data: *const u8, lens_data: *const u32, lens_len: u32, result: *mut u8);
 	fn ext_chain_id() -> u64;
 	fn ext_blake2_256(data: *const u8, len: u32, out: *mut u8);
@@ -269,10 +269,10 @@ pub fn child_storage_root(storage_key: &[u8]) -> Option<Vec<u8>> {
 }
 
 /// The current storage' changes root.
-pub fn storage_changes_root(block: u64) -> Option<[u8; 32]> {
+pub fn storage_changes_root(parent_hash: [u8; 32], parent_num: u64) -> Option<[u8; 32]> {
 	let mut result: [u8; 32] = Default::default();
 	let is_set = unsafe {
-		ext_storage_changes_root(block, result.as_mut_ptr())
+		ext_storage_changes_root(parent_hash.as_ptr(), parent_hash.len() as u32, parent_num, result.as_mut_ptr())
 	};
 
 	if is_set != 0 {
diff --git a/core/sr-primitives/src/traits.rs b/core/sr-primitives/src/traits.rs
index 809c617218f7e..28c7997a0f04f 100644
--- a/core/sr-primitives/src/traits.rs
+++ b/core/sr-primitives/src/traits.rs
@@ -276,7 +276,7 @@ pub trait Hash: 'static + MaybeSerializeDebug + Clone + Eq + PartialEq {	// Stup
 	fn storage_root() -> Self::Output;
 
 	/// Acquire the global storage changes root.
-	fn storage_changes_root(block: u64) -> Option<Self::Output>;
+	fn storage_changes_root(parent_hash: Self::Output, parent_number: u64) -> Option<Self::Output>;
 }
 
 /// Blake2-256 Hash implementation.
@@ -308,8 +308,8 @@ impl Hash for BlakeTwo256 {
 	fn storage_root() -> Self::Output {
 		runtime_io::storage_root().into()
 	}
-	fn storage_changes_root(block: u64) -> Option<Self::Output> {
-		runtime_io::storage_changes_root(block).map(Into::into)
+	fn storage_changes_root(parent_hash: Self::Output, parent_number: u64) -> Option<Self::Output> {
+		runtime_io::storage_changes_root(parent_hash.into(), parent_number).map(Into::into)
 	}
 }
 
diff --git a/core/state-machine/src/changes_trie/build.rs b/core/state-machine/src/changes_trie/build.rs
index 991b39593838a..c183f2b3cce23 100644
--- a/core/state-machine/src/changes_trie/build.rs
+++ b/core/state-machine/src/changes_trie/build.rs
@@ -25,7 +25,7 @@ use overlayed_changes::OverlayedChanges;
 use trie_backend_essence::{TrieBackendStorage, TrieBackendEssence};
 use changes_trie::build_iterator::digest_build_iterator;
 use changes_trie::input::{InputKey, InputPair, DigestIndex, ExtrinsicIndex};
-use changes_trie::{Configuration, Storage};
+use changes_trie::{AnchorBlockId, Configuration, Storage};
 
 /// Prepare input pairs for building a changes trie of given block.
 ///
@@ -37,7 +37,7 @@ pub fn prepare_input<'a, B, S, H>(
 	backend: &B,
 	storage: Option<&'a S>,
 	changes: &OverlayedChanges,
-	block: u64,
+	parent: &'a AnchorBlockId<H::Out>,
 ) -> Result<Option<Vec<InputPair>>, String>
 	where
 		B: Backend<H>,
@@ -54,10 +54,10 @@ pub fn prepare_input<'a, B, S, H>(
 	let mut input = Vec::new();
 	input.extend(prepare_extrinsics_input(
 		backend,
-		block,
+		parent.number + 1,
 		changes)?);
 	input.extend(prepare_digest_input::<_, H>(
-		block,
+		parent,
 		config,
 		storage)?);
 
@@ -73,7 +73,6 @@ fn prepare_extrinsics_input<B, H>(
 	where
 		B: Backend<H>,
 		H: Hasher,
-
 {
 	let mut extrinsic_map = BTreeMap::<Vec<u8>, BTreeSet<u32>>::new();
 	for (key, val) in changes.prospective.top.iter().chain(changes.committed.top.iter()) {
@@ -103,19 +102,19 @@ fn prepare_extrinsics_input<B, H>(
 
 /// Prepare DigestIndex input pairs.
 fn prepare_digest_input<'a, S, H>(
-	block: u64,
+	parent: &'a AnchorBlockId<H::Out>,
 	config: &Configuration,
 	storage: &'a S
-) -> Result<impl Iterator<Item=InputPair>, String>
+) -> Result<impl Iterator<Item=InputPair> + 'a, String>
 	where
 		S: Storage<H>,
 		&'a S: TrieBackendStorage<H>,
 		H: Hasher,
-		H::Out: HeapSizeOf,
+		H::Out: 'a + HeapSizeOf,
 {
 	let mut digest_map = BTreeMap::<Vec<u8>, BTreeSet<u64>>::new();
-	for digest_build_block in digest_build_iterator(config, block) {
-		let trie_root = storage.root(digest_build_block)?;
+	for digest_build_block in digest_build_iterator(config, parent.number + 1) {
+		let trie_root = storage.root(parent, digest_build_block)?;
 		let trie_root = trie_root.ok_or_else(|| format!("No changes trie root for block {}", digest_build_block))?;
 		let trie_storage = TrieBackendEssence::<_, H>::new(storage, trie_root);
 
@@ -136,7 +135,7 @@ fn prepare_digest_input<'a, S, H>(
 
 	Ok(digest_map.into_iter()
 		.map(move |(key, set)| InputPair::DigestIndex(DigestIndex {
-			block,
+			block: parent.number + 1,
 			key
 		}, set.into_iter().collect())))
 }
@@ -228,7 +227,7 @@ mod test {
 	#[test]
 	fn build_changes_trie_nodes_on_non_digest_block() {
 		let (backend, storage, changes) = prepare_for_build();
-		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, 5).unwrap();
+		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, &AnchorBlockId { hash: Default::default(), number: 4 }).unwrap();
 		assert_eq!(changes_trie_nodes, Some(vec![
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 5, key: vec![100] }, vec![0, 2, 3]),
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 5, key: vec![101] }, vec![1]),
@@ -239,7 +238,7 @@ mod test {
 	#[test]
 	fn build_changes_trie_nodes_on_digest_block_l1() {
 		let (backend, storage, changes) = prepare_for_build();
-		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, 4).unwrap();
+		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, &AnchorBlockId { hash: Default::default(), number: 3 }).unwrap();
 		assert_eq!(changes_trie_nodes, Some(vec![
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 4, key: vec![100] }, vec![0, 2, 3]),
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 4, key: vec![101] }, vec![1]),
@@ -255,7 +254,7 @@ mod test {
 	#[test]
 	fn build_changes_trie_nodes_on_digest_block_l2() {
 		let (backend, storage, changes) = prepare_for_build();
-		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, 16).unwrap();
+		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, &AnchorBlockId { hash: Default::default(), number: 15 }).unwrap();
 		assert_eq!(changes_trie_nodes, Some(vec![
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 16, key: vec![100] }, vec![0, 2, 3]),
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 16, key: vec![101] }, vec![1]),
@@ -279,7 +278,7 @@ mod test {
 			extrinsics: Some(vec![1].into_iter().collect())
 		});
 
-		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, 4).unwrap();
+		let changes_trie_nodes = prepare_input(&backend, Some(&storage), &changes, &AnchorBlockId { hash: Default::default(), number: 3 }).unwrap();
 		assert_eq!(changes_trie_nodes, Some(vec![
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 4, key: vec![100] }, vec![0, 2, 3]),
 			InputPair::ExtrinsicIndex(ExtrinsicIndex { block: 4, key: vec![101] }, vec![1]),
diff --git a/core/state-machine/src/changes_trie/changes_iterator.rs b/core/state-machine/src/changes_trie/changes_iterator.rs
index 8b4d2bd54070b..e8bd1e7db6b1a 100644
--- a/core/state-machine/src/changes_trie/changes_iterator.rs
+++ b/core/state-machine/src/changes_trie/changes_iterator.rs
@@ -23,7 +23,7 @@ use codec::{Decode, Encode};
 use hash_db::{HashDB, Hasher};
 use heapsize::HeapSizeOf;
 use substrate_trie::{Recorder, MemoryDB};
-use changes_trie::{Configuration, RootsStorage, Storage};
+use changes_trie::{AnchorBlockId, Configuration, RootsStorage, Storage};
 use changes_trie::input::{DigestIndex, ExtrinsicIndex, DigestIndexValue, ExtrinsicIndexValue};
 use changes_trie::storage::{TrieBackendAdapter, InMemoryStorage};
 use proving_backend::ProvingBackendEssence;
@@ -35,7 +35,7 @@ pub fn key_changes<S: Storage<H>, H: Hasher>(
 	config: &Configuration,
 	storage: &S,
 	begin: u64,
-	end: u64,
+	end: &AnchorBlockId<H::Out>,
 	max: u64,
 	key: &[u8],
 ) -> Result<Vec<(u64, u32)>, String> where H::Out: HeapSizeOf {
@@ -46,7 +46,7 @@ pub fn key_changes<S: Storage<H>, H: Hasher>(
 			storage,
 			begin,
 			end,
-			surface: surface_iterator(config, max, begin, end)?,
+			surface: surface_iterator(config, max, begin, end.number)?,
 
 			extrinsics: Default::default(),
 			blocks: Default::default(),
@@ -62,7 +62,7 @@ pub fn key_changes_proof<S: Storage<H>, H: Hasher>(
 	config: &Configuration,
 	storage: &S,
 	begin: u64,
-	end: u64,
+	end: &AnchorBlockId<H::Out>,
 	max: u64,
 	key: &[u8],
 ) -> Result<Vec<Vec<u8>>, String> where H::Out: HeapSizeOf {
@@ -73,7 +73,7 @@ pub fn key_changes_proof<S: Storage<H>, H: Hasher>(
 			storage,
 			begin,
 			end,
-			surface: surface_iterator(config, max, begin, end)?,
+			surface: surface_iterator(config, max, begin, end.number)?,
 
 			extrinsics: Default::default(),
 			blocks: Default::default(),
@@ -98,7 +98,7 @@ pub fn key_changes_proof_check<S: RootsStorage<H>, H: Hasher>(
 	roots_storage: &S,
 	proof: Vec<Vec<u8>>,
 	begin: u64,
-	end: u64,
+	end: &AnchorBlockId<H::Out>,
 	max: u64,
 	key: &[u8]
 ) -> Result<Vec<(u64, u32)>, String> where H::Out: HeapSizeOf {
@@ -115,7 +115,7 @@ pub fn key_changes_proof_check<S: RootsStorage<H>, H: Hasher>(
 			storage: &proof_db,
 			begin,
 			end,
-			surface: surface_iterator(config, max, begin, end)?,
+			surface: surface_iterator(config, max, begin, end.number)?,
 
 			extrinsics: Default::default(),
 			blocks: Default::default(),
@@ -174,12 +174,12 @@ impl<'a> Iterator for SurfaceIterator<'a> {
 
 /// Drilldown iterator - receives 'digest points' from surface iterator and explores
 /// every point until extrinsic is found.
-pub struct DrilldownIteratorEssence<'a, RS: 'a + RootsStorage<H>, S: 'a + Storage<H>, H: Hasher> {
+pub struct DrilldownIteratorEssence<'a, RS: 'a + RootsStorage<H>, S: 'a + Storage<H>, H: Hasher> where H::Out: 'a {
 	key: &'a [u8],
 	roots_storage: &'a RS,
 	storage: &'a S,
 	begin: u64,
-	end: u64,
+	end: &'a AnchorBlockId<H::Out>,
 	surface: SurfaceIterator<'a>,
 
 	extrinsics: VecDeque<(u64, u32)>,
@@ -213,14 +213,14 @@ impl<'a, RS: 'a + RootsStorage<H>, S: Storage<H>, H: Hasher> DrilldownIteratorEs
 				// not having a changes trie root is an error because:
 				// we never query roots for future blocks
 				// AND trie roots for old blocks are known (both on full + light node)
-				let trie_root = self.roots_storage.root(block)?
+				let trie_root = self.roots_storage.root(&self.end, block)?
 					.ok_or_else(|| format!("Changes trie root for block {} is not found", block))?;
 
 				// only return extrinsics for blocks before self.max
 				// most of blocks will be filtered out beore pushing to `self.blocks`
 				// here we just throwing away changes at digest blocks we're processing
 				debug_assert!(block >= self.begin, "We shall not touch digests earlier than a range' begin");
-				if block <= self.end {
+				if block <= self.end.number {
 					let extrinsics_key = ExtrinsicIndex { block, key: self.key.to_vec() }.encode();
 					let extrinsics = trie_reader(&self.storage, trie_root, &extrinsics_key);
 					if let Some(extrinsics) = extrinsics? {
@@ -239,7 +239,7 @@ impl<'a, RS: 'a + RootsStorage<H>, S: Storage<H>, H: Hasher> DrilldownIteratorEs
 						// filter level0 blocks here because we tend to use digest blocks,
 						// AND digest block changes could also include changes for out-of-range blocks
 						let begin = self.begin;
-						let end = self.end;
+						let end = self.end.number;
 						self.blocks.extend(blocks.into_iter()
 							.rev()
 							.filter(|b| level > 1 || (*b >= begin && *b <= end))
@@ -261,7 +261,7 @@ impl<'a, RS: 'a + RootsStorage<H>, S: Storage<H>, H: Hasher> DrilldownIteratorEs
 }
 
 /// Exploring drilldown operator.
-struct DrilldownIterator<'a, RS: 'a + RootsStorage<H>, S: 'a + Storage<H>, H: Hasher> {
+struct DrilldownIterator<'a, RS: 'a + RootsStorage<H>, S: 'a + Storage<H>, H: Hasher> where H::Out: 'a {
 	essence: DrilldownIteratorEssence<'a, RS, S, H>,
 }
 
@@ -278,7 +278,7 @@ impl<'a, RS: 'a + RootsStorage<H>, S: Storage<H>, H: Hasher> Iterator
 }
 
 /// Proving drilldown iterator.
-struct ProvingDrilldownIterator<'a, RS: 'a + RootsStorage<H>, S: 'a + Storage<H>, H: Hasher> {
+struct ProvingDrilldownIterator<'a, RS: 'a + RootsStorage<H>, S: 'a + Storage<H>, H: Hasher> where H::Out: 'a {
 	essence: DrilldownIteratorEssence<'a, RS, S, H>,
 	proof_recorder: RefCell<Recorder<H::Out>>,
 }
@@ -427,23 +427,23 @@ mod tests {
 	fn drilldown_iterator_works() {
 		let (config, storage) = prepare_for_drilldown();
 		let drilldown_result = key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 0, 16, 16, &[42]);
+			&config, &storage, 0, &AnchorBlockId { hash: Default::default(), number: 16 }, 16, &[42]);
 		assert_eq!(drilldown_result, Ok(vec![(8, 2), (8, 1), (6, 3), (3, 0)]));
 
 		let drilldown_result = key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 0, 2, 4, &[42]);
+			&config, &storage, 0, &AnchorBlockId { hash: Default::default(), number: 2 }, 4, &[42]);
 		assert_eq!(drilldown_result, Ok(vec![]));
 
 		let drilldown_result = key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 0, 3, 4, &[42]);
+			&config, &storage, 0, &AnchorBlockId { hash: Default::default(), number: 3 }, 4, &[42]);
 		assert_eq!(drilldown_result, Ok(vec![(3, 0)]));
 
 		let drilldown_result = key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 7, 8, 8, &[42]);
+			&config, &storage, 7, &AnchorBlockId { hash: Default::default(), number: 8 }, 8, &[42]);
 		assert_eq!(drilldown_result, Ok(vec![(8, 2), (8, 1)]));
 
 		let drilldown_result = key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 5, 7, 8, &[42]);
+			&config, &storage, 5, &AnchorBlockId { hash: Default::default(), number: 7 }, 8, &[42]);
 		assert_eq!(drilldown_result, Ok(vec![(6, 3)]));
 	}
 
@@ -453,16 +453,16 @@ mod tests {
 		storage.clear_storage();
 
 		assert!(key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 0, 100, 1000, &[42]).is_err());
+			&config, &storage, 0, &AnchorBlockId { hash: Default::default(), number: 100 }, 1000, &[42]).is_err());
 	}
 
 	#[test]
 	fn drilldown_iterator_fails_when_range_is_invalid() {
 		let (config, storage) = prepare_for_drilldown();
 		assert!(key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 0, 100, 50, &[42]).is_err());
+			&config, &storage, 0, &AnchorBlockId { hash: Default::default(), number: 100 }, 50, &[42]).is_err());
 		assert!(key_changes::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
-			&config, &storage, 20, 10, 100, &[42]).is_err());
+			&config, &storage, 20, &AnchorBlockId { hash: Default::default(), number: 10 }, 100, &[42]).is_err());
 	}
 
 
@@ -474,7 +474,7 @@ mod tests {
 		let (remote_config, remote_storage) = prepare_for_drilldown();
 		let remote_proof = key_changes_proof::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
 			&remote_config, &remote_storage,
-			0, 16, 16, &[42]).unwrap();
+			0, &AnchorBlockId { hash: Default::default(), number: 16 }, 16, &[42]).unwrap();
 
 		// happens on local light node:
 
@@ -483,7 +483,7 @@ mod tests {
 		local_storage.clear_storage();
 		let local_result = key_changes_proof_check::<InMemoryStorage<Blake2Hasher>, Blake2Hasher>(
 			&local_config, &local_storage, remote_proof,
-			0, 16, 16, &[42]);
+			0, &AnchorBlockId { hash: Default::default(), number: 16 }, 16, &[42]);
 
 		// check that drilldown result is the same as if it was happening at the full node
 		assert_eq!(local_result, Ok(vec![(8, 2), (8, 1), (6, 3), (3, 0)]));
diff --git a/core/state-machine/src/changes_trie/mod.rs b/core/state-machine/src/changes_trie/mod.rs
index fb16cb54d60c2..1d523854ee3e3 100644
--- a/core/state-machine/src/changes_trie/mod.rs
+++ b/core/state-machine/src/changes_trie/mod.rs
@@ -58,10 +58,20 @@ use trie::{DBValue, trie_root};
 /// Changes that are made outside of extrinsics are marked with this index;
 pub const NO_EXTRINSIC_INDEX: u32 = 0xffffffff;
 
+/// Block identifier that could be used to determine fork of this block.
+#[derive(Debug)]
+pub struct AnchorBlockId<Hash: ::std::fmt::Debug> {
+	/// Hash of this block.
+	pub hash: Hash,
+	/// Number of this block.
+	pub number: u64,
+}
+
 /// Changes trie storage. Provides access to trie roots and trie nodes.
 pub trait RootsStorage<H: Hasher>: Send + Sync {
-	/// Get changes trie root for given block.
-	fn root(&self, block: u64) -> Result<Option<H::Out>, String>;
+	/// Get changes trie root for the block with given number which is an ancestor (or the block
+	/// itself) of the anchor_block (i.e. anchor_block.number >= block).
+	fn root(&self, anchor: &AnchorBlockId<H::Out>, block: u64) -> Result<Option<H::Out>, String>;
 }
 
 /// Changes trie storage. Provides access to trie roots and trie nodes.
@@ -79,13 +89,13 @@ pub fn compute_changes_trie_root<'a, B: Backend<H>, S: Storage<H>, H: Hasher>(
 	backend: &B,
 	storage: Option<&'a S>,
 	changes: &OverlayedChanges,
-	block: u64,
+	parent: &'a AnchorBlockId<H::Out>,
 ) -> Option<(H::Out, Vec<(Vec<u8>, Vec<u8>)>)>
 	where
 		&'a S: TrieBackendStorage<H>,
 		H::Out: Ord + HeapSizeOf,
 {
-	let input_pairs = prepare_input::<B, S, H>(backend, storage, changes, block)
+	let input_pairs = prepare_input::<B, S, H>(backend, storage, changes, parent)
 		.expect("storage is not allowed to fail within runtime")?;
 	let transaction = input_pairs.into_iter()
 		.map(Into::into)
diff --git a/core/state-machine/src/changes_trie/prune.rs b/core/state-machine/src/changes_trie/prune.rs
index 8168a0771d315..70bae77b0273f 100644
--- a/core/state-machine/src/changes_trie/prune.rs
+++ b/core/state-machine/src/changes_trie/prune.rs
@@ -21,7 +21,7 @@ use heapsize::HeapSizeOf;
 use substrate_trie::Recorder;
 use proving_backend::ProvingBackendEssence;
 use trie_backend_essence::TrieBackendEssence;
-use changes_trie::{Configuration, Storage};
+use changes_trie::{AnchorBlockId, Configuration, Storage};
 use changes_trie::storage::TrieBackendAdapter;
 
 /// Prune obslete changes tries. Puning happens at the same block, where highest
@@ -33,21 +33,21 @@ pub fn prune<S: Storage<H>, H: Hasher, F: FnMut(H::Out)>(
 	config: &Configuration,
 	storage: &S,
 	min_blocks_to_keep: u64,
-	current_block: u64,
+	current_block: &AnchorBlockId<H::Out>,
 	mut remove_trie_node: F,
 )
 	where
 		H::Out: HeapSizeOf,
 {
 	// we only CAN prune at block where max-level-digest is created
-	let digest_interval = match config.digest_level_at_block(current_block) {
+	let digest_interval = match config.digest_level_at_block(current_block.number) {
 		Some((digest_level, digest_interval, _)) if digest_level == config.digest_levels =>
 			digest_interval,
 		_ => return,
 	};
 
 	// select range for pruning
-	let (first, last) = match pruning_range(min_blocks_to_keep, current_block, digest_interval) {
+	let (first, last) = match pruning_range(min_blocks_to_keep, current_block.number, digest_interval) {
 		Some((first, last)) => (first, last),
 		None => return,
 	};
@@ -55,7 +55,7 @@ pub fn prune<S: Storage<H>, H: Hasher, F: FnMut(H::Out)>(
 	// delete changes trie for every block in range
 	// TODO: limit `max_digest_interval` so that this cycle won't involve huge ranges
 	for block in first..last+1 {
-		let root = match storage.root(block) {
+		let root = match storage.root(current_block, block) {
 			Ok(Some(root)) => root,
 			Ok(None) => continue,
 			Err(error) => {
@@ -139,7 +139,7 @@ mod tests {
 			H::Out: HeapSizeOf,
 	{
 		let mut pruned_trie_nodes = HashSet::new();
-		prune(config, storage, min_blocks_to_keep, current_block,
+		prune(config, storage, min_blocks_to_keep, &AnchorBlockId { hash: Default::default(), number: current_block },
 			|node| { pruned_trie_nodes.insert(node); });
 		pruned_trie_nodes
 	}
diff --git a/core/state-machine/src/changes_trie/storage.rs b/core/state-machine/src/changes_trie/storage.rs
index 1cdd03841e1cf..088b605e9cc16 100644
--- a/core/state-machine/src/changes_trie/storage.rs
+++ b/core/state-machine/src/changes_trie/storage.rs
@@ -22,7 +22,7 @@ use trie::DBValue;
 use heapsize::HeapSizeOf;
 use trie::MemoryDB;
 use parking_lot::RwLock;
-use changes_trie::{RootsStorage, Storage};
+use changes_trie::{AnchorBlockId, RootsStorage, Storage};
 use trie_backend_essence::TrieBackendStorage;
 
 #[cfg(test)]
@@ -110,7 +110,7 @@ impl<H: Hasher> InMemoryStorage<H> where H::Out: HeapSizeOf {
 }
 
 impl<H: Hasher> RootsStorage<H> for InMemoryStorage<H> where H::Out: HeapSizeOf {
-	fn root(&self, block: u64) -> Result<Option<H::Out>, String> {
+	fn root(&self, _anchor_block: &AnchorBlockId<H::Out>, block: u64) -> Result<Option<H::Out>, String> {
 		Ok(self.data.read().roots.get(&block).cloned())
 	}
 }
diff --git a/core/state-machine/src/ext.rs b/core/state-machine/src/ext.rs
index b03ed28250608..1bcb3fb732b1f 100644
--- a/core/state-machine/src/ext.rs
+++ b/core/state-machine/src/ext.rs
@@ -18,7 +18,7 @@
 
 use std::{error, fmt, cmp::Ord};
 use backend::{Backend, Consolidate};
-use changes_trie::{Storage as ChangesTrieStorage, compute_changes_trie_root};
+use changes_trie::{AnchorBlockId, Storage as ChangesTrieStorage, compute_changes_trie_root};
 use {Externalities, OverlayedChanges};
 use hash_db::Hasher;
 use primitives::storage::well_known_keys::is_child_storage_key;
@@ -288,12 +288,12 @@ where
 		Some(self.child_storage_root_transaction(storage_key).0)
 	}
 
-	fn storage_changes_root(&mut self, block: u64) -> Option<H::Out> {
+	fn storage_changes_root(&mut self, parent: H::Out, parent_num: u64) -> Option<H::Out> {
 		let root_and_tx = compute_changes_trie_root::<_, T, H>(
 			self.backend,
 			self.changes_trie_storage.clone(),
 			self.overlay,
-			block,
+			&AnchorBlockId { hash: parent, number: parent_num },
 		);
 		let root_and_tx = root_and_tx.map(|(root, changes)| {
 			let mut calculated_root = Default::default();
@@ -305,7 +305,7 @@ where
 				}
 			}
 
-			(block, mdb, root)
+			(parent_num + 1, mdb, root)
 		});
 		let root = root_and_tx.as_ref().map(|(_, _, root)| root.clone());
 		self.changes_trie_transaction = root_and_tx;
@@ -353,7 +353,7 @@ mod tests {
 		let mut overlay = prepare_overlay_with_changes();
 		let backend = TestBackend::default();
 		let mut ext = TestExt::new(&mut overlay, &backend, None);
-		assert_eq!(ext.storage_changes_root(100), None);
+		assert_eq!(ext.storage_changes_root(Default::default(), 100), None);
 	}
 
 	#[test]
@@ -363,7 +363,7 @@ mod tests {
 		let storage = TestChangesTrieStorage::new();
 		let backend = TestBackend::default();
 		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage));
-		assert_eq!(ext.storage_changes_root(100), None);
+		assert_eq!(ext.storage_changes_root(Default::default(), 100), None);
 	}
 
 	#[test]
@@ -372,7 +372,7 @@ mod tests {
 		let storage = TestChangesTrieStorage::new();
 		let backend = TestBackend::default();
 		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage));
-		assert_eq!(ext.storage_changes_root(100),
+		assert_eq!(ext.storage_changes_root(Default::default(), 99),
 			Some(hex!("5b829920b9c8d554a19ee2a1ba593c4f2ee6fc32822d083e04236d693e8358d5").into()));
 	}
 
@@ -383,7 +383,7 @@ mod tests {
 		let storage = TestChangesTrieStorage::new();
 		let backend = TestBackend::default();
 		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage));
-		assert_eq!(ext.storage_changes_root(100),
+		assert_eq!(ext.storage_changes_root(Default::default(), 99),
 			Some(hex!("bcf494e41e29a15c9ae5caa053fe3cb8b446ee3e02a254efbdec7a19235b76e4").into()));
 	}
 }
diff --git a/core/state-machine/src/lib.rs b/core/state-machine/src/lib.rs
index 7b0f3690d8d49..e88b3f370a773 100644
--- a/core/state-machine/src/lib.rs
+++ b/core/state-machine/src/lib.rs
@@ -53,7 +53,9 @@ pub use trie::{TrieMut, TrieDBMut, DBValue, MemoryDB};
 pub use testing::TestExternalities;
 pub use ext::Ext;
 pub use backend::Backend;
-pub use changes_trie::{Storage as ChangesTrieStorage,
+pub use changes_trie::{
+	AnchorBlockId as ChangesTrieAnchorBlockId,
+	Storage as ChangesTrieStorage,
 	RootsStorage as ChangesTrieRootsStorage,
 	InMemoryStorage as InMemoryChangesTrieStorage,
 	key_changes, key_changes_proof, key_changes_proof_check,
@@ -154,8 +156,8 @@ pub trait Externalities<H: Hasher> {
 	/// Returns None if key provided is not a storage key. This can due to not being started with CHILD_STORAGE_KEY_PREFIX, or the trie implementation regards the key as invalid.
 	fn child_storage_root(&mut self, storage_key: &[u8]) -> Option<Vec<u8>>;
 
-	/// Get the change trie root of the current storage overlay at given block.
-	fn storage_changes_root(&mut self, block: u64) -> Option<H::Out> where H::Out: Ord;
+	/// Get the change trie root of the current storage overlay at a block wth given parent.
+	fn storage_changes_root(&mut self, parent: H::Out, parent_num: u64) -> Option<H::Out> where H::Out: Ord;
 }
 
 /// Code execution engine.
diff --git a/core/state-machine/src/testing.rs b/core/state-machine/src/testing.rs
index 75ad342b6bbc2..876a190a966a9 100644
--- a/core/state-machine/src/testing.rs
+++ b/core/state-machine/src/testing.rs
@@ -22,7 +22,7 @@ use hash_db::Hasher;
 use heapsize::HeapSizeOf;
 use trie::trie_root;
 use backend::InMemory;
-use changes_trie::{compute_changes_trie_root, InMemoryStorage as ChangesTrieInMemoryStorage};
+use changes_trie::{compute_changes_trie_root, InMemoryStorage as ChangesTrieInMemoryStorage, AnchorBlockId};
 use primitives::storage::well_known_keys::CHANGES_TRIE_CONFIG;
 use super::{Externalities, OverlayedChanges};
 
@@ -136,12 +136,12 @@ impl<H: Hasher> Externalities<H> for TestExternalities<H> where H::Out: Ord + He
 		None
 	}
 
-	fn storage_changes_root(&mut self, block: u64) -> Option<H::Out> {
+	fn storage_changes_root(&mut self, parent: H::Out, parent_num: u64) -> Option<H::Out> {
 		compute_changes_trie_root::<_, _, H>(
 			&InMemory::default(),
 			Some(&self.changes_trie_storage),
 			&self.changes,
-			block,
+			&AnchorBlockId { hash: parent, number: parent_num },
 		).map(|(root, _)| root.clone())
 	}
 }
diff --git a/core/test-runtime/src/system.rs b/core/test-runtime/src/system.rs
index a3041647d43f2..3703fb553e685 100644
--- a/core/test-runtime/src/system.rs
+++ b/core/test-runtime/src/system.rs
@@ -93,7 +93,7 @@ pub fn execute_block(block: Block) {
 
 	// check digest
 	let mut digest = Digest::default();
-	if let Some(storage_changes_root) = storage_changes_root(header.number) {
+	if let Some(storage_changes_root) = storage_changes_root(header.parent_hash.into(), header.number - 1) {
 		digest.push(generic::DigestItem::ChangesTrieRoot::<Hash, u64>(storage_changes_root.into()));
 	}
 	assert!(digest == header.digest, "Header digest items must match that calculated.");
@@ -160,7 +160,7 @@ pub fn finalise_block() -> Header {
 	let number = <Number>::take();
 	let parent_hash = <ParentHash>::take();
 	let storage_root = BlakeTwo256::storage_root();
-	let storage_changes_root = BlakeTwo256::storage_changes_root(number);
+	let storage_changes_root = BlakeTwo256::storage_changes_root(parent_hash, number - 1);
 
 	let mut digest = Digest::default();
 	if let Some(storage_changes_root) = storage_changes_root {
diff --git a/core/test-runtime/wasm/target/wasm32-unknown-unknown/release/substrate_test_runtime.compact.wasm b/core/test-runtime/wasm/target/wasm32-unknown-unknown/release/substrate_test_runtime.compact.wasm
index bbac245c7b462..c526eacd1f6de 100644
Binary files a/core/test-runtime/wasm/target/wasm32-unknown-unknown/release/substrate_test_runtime.compact.wasm and b/core/test-runtime/wasm/target/wasm32-unknown-unknown/release/substrate_test_runtime.compact.wasm differ
diff --git a/node/executor/src/lib.rs b/node/executor/src/lib.rs
index fe491c7cfdbaf..704f2d342f276 100644
--- a/node/executor/src/lib.rs
+++ b/node/executor/src/lib.rs
@@ -734,7 +734,7 @@ mod tests {
 		let mut t = new_test_ext(true);
 		Executor::new().call(&mut t, 8, COMPACT_CODE, "execute_block", &block1(true).0, true).0.unwrap();
 
-		assert!(t.storage_changes_root(1).is_some());
+		assert!(t.storage_changes_root(Default::default(), 0).is_some());
 	}
 
 	#[test]
@@ -742,6 +742,6 @@ mod tests {
 		let mut t = new_test_ext(true);
 		WasmExecutor::new().call(&mut t, 8, COMPACT_CODE, "execute_block", &block1(true).0).unwrap();
 
-		assert!(t.storage_changes_root(1).is_some());
+		assert!(t.storage_changes_root(Default::default(), 0).is_some());
 	}
 }
diff --git a/node/runtime/wasm/target/wasm32-unknown-unknown/release/node_runtime.compact.wasm b/node/runtime/wasm/target/wasm32-unknown-unknown/release/node_runtime.compact.wasm
index aee72d47e77ac..aafdeedceb1d9 100644
Binary files a/node/runtime/wasm/target/wasm32-unknown-unknown/release/node_runtime.compact.wasm and b/node/runtime/wasm/target/wasm32-unknown-unknown/release/node_runtime.compact.wasm differ
diff --git a/srml/system/src/lib.rs b/srml/system/src/lib.rs
index eccd99a98c7cd..c3cffda04f0f0 100644
--- a/srml/system/src/lib.rs
+++ b/srml/system/src/lib.rs
@@ -284,7 +284,7 @@ impl<T: Trait> Module<T> {
 		let mut digest = <Digest<T>>::take();
 		let extrinsics_root = <ExtrinsicsRoot<T>>::take();
 		let storage_root = T::Hashing::storage_root();
-		let storage_changes_root = T::Hashing::storage_changes_root(number.as_());
+		let storage_changes_root = T::Hashing::storage_changes_root(parent_hash, number.as_() - 1);
 
 		// we can't compute changes trie root earlier && put it to the Digest
 		// because it will include all currently existing temporaries