diff --git a/mypy_boto3_builder/parsers/shape_parser.py b/mypy_boto3_builder/parsers/shape_parser.py
index 55f3f06f..20292a70 100644
--- a/mypy_boto3_builder/parsers/shape_parser.py
+++ b/mypy_boto3_builder/parsers/shape_parser.py
@@ -77,6 +77,7 @@
     get_type_def_name,
     xform_name,
 )
+from mypy_boto3_builder.utils.type_checks import is_union
 
 
 class ShapeParser:
@@ -1309,8 +1310,11 @@ def convert_input_arguments_to_unions(self, methods: Sequence[Method]) -> None:
             )
             for type_annotation in parent_type_annotations:
                 parents = type_annotation.find_type_annotation_parents(input_typed_dict)
+                if not parents:
+                    continue
+
                 for parent in sorted(parents):
-                    if parent is union_type_annotation:
+                    if is_union(parent) and parent.name == union_name:
                         continue
                     self.logger.debug(
                         f"Adding output shape to {parent.render()} type:"
diff --git a/mypy_boto3_builder/type_annotations/type_parent.py b/mypy_boto3_builder/type_annotations/type_parent.py
index e5d0d929..a00bcff4 100644
--- a/mypy_boto3_builder/type_annotations/type_parent.py
+++ b/mypy_boto3_builder/type_annotations/type_parent.py
@@ -41,26 +41,50 @@ def get_children_types(self) -> set[FakeAnnotation]:
     def find_type_annotation_parents(
         self,
         type_annotation: FakeAnnotation,
-        skip: Iterable[FakeAnnotation] = (),
     ) -> "set[TypeParent]":
         """
         Check recursively if child is present in type def.
         """
-        result: set[TypeParent] = set()
-        for child_type in self.iterate_children_type_annotations():
-            if child_type == type_annotation:
-                result.add(self)
-            if not isinstance(child_type, TypeParent):
-                continue
+        return self.find_type_annotation_parent_map({type_annotation}).get(type_annotation) or set()
 
-            if child_type in skip:
-                continue
+    def find_type_annotation_parent_map(
+        self, type_annotations: Iterable[FakeAnnotation]
+    ) -> "dict[FakeAnnotation, set[TypeParent]]":
+        """
+        Check recursively if children are present in type def.
+
+        Can be used for non-overlapping type annotations.
+        """
+        result: dict[FakeAnnotation, set[TypeParent]] = {}
+        for parent in self.find_parents():
+            for child_type in parent.iterate_children_type_annotations():
+                if child_type not in type_annotations:
+                    continue
+
+                if child_type not in result:
+                    result[child_type] = set()
+
+                result[child_type].add(parent)
+
+        return result
+
+    def find_parents(self) -> "set[TypeParent]":
+        """
+        Find all parents recursively including self.
+        """
+        result: set[TypeParent] = {self}
+        stack: list[TypeParent] = [self]
+
+        while stack:
+            current = stack.pop()
+            for child_type in current.iterate_children_type_annotations():
+                if not isinstance(child_type, TypeParent):
+                    continue
+                if child_type in result:
+                    continue
 
-            parents = child_type.find_type_annotation_parents(
-                type_annotation,
-                skip={*skip, child_type},
-            )
-            result.update(parents)
+                result.add(child_type)
+                stack.append(child_type)
 
         return result
 
diff --git a/tests/type_annotations/test_type_subscript.py b/tests/type_annotations/test_type_subscript.py
index e9a08a63..5145431a 100644
--- a/tests/type_annotations/test_type_subscript.py
+++ b/tests/type_annotations/test_type_subscript.py
@@ -55,6 +55,13 @@ def test_find_type_annotation_parents(self) -> None:
         assert outer.find_type_annotation_parents(Type.str) == {outer}
         assert outer.find_type_annotation_parents(Type.List) == set()
 
+    def test_find_type_annotation_parent_map(self) -> None:
+        inner = TypeSubscript(Type.List, [Type.int])
+        outer = TypeSubscript(Type.Dict, [Type.str, inner])
+        assert outer.find_type_annotation_parent_map([Type.int]) == {Type.int: {inner}}
+        assert outer.find_type_annotation_parent_map([Type.str]) == {Type.str: {outer}}
+        assert outer.find_type_annotation_parent_map([Type.List]) == {}
+
     def test_replace_child(self) -> None:
         inner = TypeSubscript(Type.List, [Type.int])
         outer = TypeSubscript(Type.Dict, [Type.str, inner])