diff --git a/mypy/server/astmerge.py b/mypy/server/astmerge.py
index 5e37592..6085308 100644
--- a/mypy/server/astmerge.py
+++ b/mypy/server/astmerge.py
@@ -400,6 +400,8 @@
         # tables separately, unlike normal classes.
         self.process_type_info(info)
         for name, node in info.names.items():
+            if isinstance(node.node, TypeInfo):
+                continue  # There might be nested classes in some cases, skip them
             if node.node:
                 node.node.accept(self)
 
diff --git a/test-data/unit/fine-grained.test b/test-data/unit/fine-grained.test
index 66c5ee4..62b035b 100644
--- a/test-data/unit/fine-grained.test
+++ b/test-data/unit/fine-grained.test
@@ -10192,23 +10192,25 @@
 from typing import NamedTuple
 
 class NT(NamedTuple):
-    class C: ...
+    class C: ...  # classes are fine
     x: int
     y: int
+    assert True  # assert statements are not allowed
 
 [file m.py.2]
 from typing import NamedTuple
 
 class NT(NamedTuple):
-    class C: ...
+    class C: ...  # classes are fine
     x: int
     y: int
+    assert True  # assert statements are not allowed
 # change
 [builtins fixtures/tuple.pyi]
 [out]
-m.py:4: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"
+m.py:7: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"
 ==
-m.py:4: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"
+m.py:7: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"
 
 [case testNamedTupleNestedClassRecheck]
 import n