diff --git a/src/pyproject_fmt/formatter/util.py b/src/pyproject_fmt/formatter/util.py
index dba1f59..32383f5 100644
--- a/src/pyproject_fmt/formatter/util.py
+++ b/src/pyproject_fmt/formatter/util.py
@@ -8,6 +8,7 @@
 from tomlkit.container import OutOfOrderTableProxy
 from tomlkit.items import (
     AbstractTable,
+    AoT,
     Array,
     Comment,
     Item,
@@ -108,8 +109,15 @@ def sorted_array(
 
 def ensure_newline_at_end(body: Table) -> None:
     content = body
-    while content.value.body and isinstance(content.value.body[-1][1], Table):
-        content = content.value.body[-1][1]
+    while True:
+        if isinstance(content, AoT) and content.value and isinstance(content[-1], (AoT, Table)):
+            content = content[-1]
+        elif isinstance(content, Table) and content.value.body and isinstance(content.value.body[-1][1], (AoT, Table)):
+            content = content.value.body[-1][1]
+        else:  # pragma: no cover
+            # coverage has a bug on python < 3.10, seeing this line as uncovered
+            # https://github.com/nedbat/coveragepy/issues/1480
+            break
     whitespace = Whitespace("\n")
     insert_body = content.value.body
     if insert_body and isinstance(insert_body[-1][1], Whitespace):
diff --git a/tests/formatter/test_tools.py b/tests/formatter/test_tools.py
index 3de4cfe..0497daf 100644
--- a/tests/formatter/test_tools.py
+++ b/tests/formatter/test_tools.py
@@ -48,3 +48,40 @@ def test_tools_ordering(fmt: Fmt) -> None:
     a = 0
         """
     fmt(fmt_tools, content, expected)
+
+
+def test_sub_table_newline(fmt: Fmt) -> None:
+    content = """
+    [tool.mypy]
+    a = 0
+
+    [[tool.mypy.overrides]]
+    a = 1
+    [tool.something-else]
+    b = 0
+    """
+    expected = """
+    [tool.mypy]
+    a = 0
+
+    [[tool.mypy.overrides]]
+    a = 1
+
+    [tool.something-else]
+    b = 0
+    """
+    fmt(fmt_tools, content, expected)
+
+
+def test_sub_table_no_op(fmt: Fmt) -> None:
+    content = """
+    [tool.mypy]
+    a = 0
+
+    [[tool.mypy.overrides]]
+    a = 1
+
+    [tool.something-else]
+    b = 0
+    """
+    fmt(fmt_tools, content, content)
diff --git a/whitelist.txt b/whitelist.txt
index d335dd8..e1097a0 100644
--- a/whitelist.txt
+++ b/whitelist.txt
@@ -1,3 +1,4 @@
+Ao
 autoclass
 autodoc
 canonicalize