diff --git a/tests/test_generate_popular_node_signatures.py b/tests/test_generate_popular_node_signatures.py
index 62cbb02..3fe7f4c 100644
--- a/tests/test_generate_popular_node_signatures.py
+++ b/tests/test_generate_popular_node_signatures.py
@@ -718,6 +718,54 @@ NODE_CLASS_MAPPINGS = {
         self.assertEqual({}, result["nodes"])
         self.assertEqual("no_static_nodes", result["pack"]["status"])
 
+    def test_subscript_assignment_to_return_names_skips_node(self):
+        source = '''
+class SubscriptMutatedReturnNamesNode:
+    RETURN_TYPES = ("IMAGE",)
+    RETURN_NAMES = ["image"]
+    RETURN_NAMES[0] = "mask"
+
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "image": ("IMAGE",),
+            },
+        }
+
+
+NODE_CLASS_MAPPINGS = {
+    "SubscriptMutatedReturnNamesNode": SubscriptMutatedReturnNamesNode,
+}
+'''
+        result = self._extract_source(source, "subscript-mutated-return-names-pack")
+
+        self.assertEqual({}, result["nodes"])
+        self.assertEqual("no_static_nodes", result["pack"]["status"])
+
+    def test_missing_return_names_is_allowed(self):
+        source = '''
+class MissingReturnNamesNode:
+    RETURN_TYPES = ("IMAGE",)
+
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "image": ("IMAGE",),
+            },
+        }
+
+
+NODE_CLASS_MAPPINGS = {
+    "MissingReturnNamesNode": MissingReturnNamesNode,
+}
+'''
+        result = self._extract_source(source, "missing-return-names-pack")
+
+        self.assertEqual([], result["nodes"]["MissingReturnNamesNode"]["output_names"])
+        self.assertEqual("ok", result["pack"]["status"])
+
     def test_final_static_return_types_assignment_wins(self):
         source = '''
 class FinalReturnTypesNode:
diff --git a/tools/generate_popular_node_signatures.py b/tools/generate_popular_node_signatures.py
index 12f9dd0..db5c4c5 100644
--- a/tools/generate_popular_node_signatures.py
+++ b/tools/generate_popular_node_signatures.py
@@ -419,8 +419,10 @@ def _class_attr(cls, name, env):
             continue
         if name in _bound_names(stmt):
             value = _INVALID
-    if value in (_MISSING, _INVALID):
+    if value is _MISSING:
         return None
+    if value is _INVALID:
+        return _INVALID
     return value
 
 
@@ -539,6 +541,8 @@ def _signature_from_class(node_type, cls, display, pack_meta, env):
     input_types = _input_types(cls, env)
     return_types = _class_attr(cls, "RETURN_TYPES", env)
     return_names = _class_attr(cls, "RETURN_NAMES", env)
+    if return_types is _INVALID or return_names is _INVALID:
+        return None
     if not isinstance(input_types, dict) or not isinstance(return_types, (list, tuple)):
         return None