diff --git a/apps/dav/lib/CalDAV/Activity/Provider/Base.php b/apps/dav/lib/CalDAV/Activity/Provider/Base.php
index 99ad903f2479d..ee9c671613061 100644
--- a/apps/dav/lib/CalDAV/Activity/Provider/Base.php
+++ b/apps/dav/lib/CalDAV/Activity/Provider/Base.php
@@ -160,7 +160,7 @@ protected function generateGroupParameter($gid) {
 		}
 
 		return [
-			'type' => 'group',
+			'type' => 'user-group',
 			'id' => $gid,
 			'name' => $this->groupDisplayNames[$gid],
 		];
diff --git a/apps/dav/tests/unit/CalDAV/Activity/Provider/BaseTest.php b/apps/dav/tests/unit/CalDAV/Activity/Provider/BaseTest.php
index 37a56f88042da..9c4f5eeb47c44 100644
--- a/apps/dav/tests/unit/CalDAV/Activity/Provider/BaseTest.php
+++ b/apps/dav/tests/unit/CalDAV/Activity/Provider/BaseTest.php
@@ -182,7 +182,7 @@ public function dataGenerateGroupParameter() {
 	 */
 	public function testGenerateGroupParameter($gid) {
 		$this->assertEquals([
-			'type' => 'group',
+			'type' => 'user-group',
 			'id' => $gid,
 			'name' => $gid,
 		], $this->invokePrivate($this->provider, 'generateGroupParameter', [$gid]));
diff --git a/apps/files_sharing/lib/Activity/Providers/Groups.php b/apps/files_sharing/lib/Activity/Providers/Groups.php
index 9a8f7164c55d7..10f52882aeb89 100644
--- a/apps/files_sharing/lib/Activity/Providers/Groups.php
+++ b/apps/files_sharing/lib/Activity/Providers/Groups.php
@@ -150,7 +150,7 @@ protected function generateGroupParameter($gid) {
 		}
 
 		return [
-			'type' => 'group',
+			'type' => 'user-group',
 			'id' => $gid,
 			'name' => $this->groupDisplayNames[$gid],
 		];
diff --git a/lib/private/RichObjectStrings/Validator.php b/lib/private/RichObjectStrings/Validator.php
index 55a50fc2a48c1..29980885cf8d7 100644
--- a/lib/private/RichObjectStrings/Validator.php
+++ b/lib/private/RichObjectStrings/Validator.php
@@ -71,11 +71,17 @@ public function validate($subject, array $parameters) {
 			foreach ($matches[1] as $parameter) {
 				if (!isset($parameters[$parameter])) {
 					throw new InvalidObjectExeption('Parameter is undefined');
-				} else {
-					$this->validateParameter($parameters[$parameter]);
 				}
 			}
 		}
+
+		foreach ($parameters as $parameter) {
+			if (!\is_array($parameter)) {
+				throw new InvalidObjectExeption('Parameter is malformed');
+			}
+
+			$this->validateParameter($parameter);
+		}
 	}
 
 	/**