diff --git a/jedi/inference/filters.py b/jedi/inference/filters.py
index f6af50dc..62782334 100644
--- a/jedi/inference/filters.py
+++ b/jedi/inference/filters.py
@@ -149,7 +149,7 @@ class ParserTreeFilter(_AbstractUsedNamesFilter):
         if parent.type == 'trailer':
             return False
         base_node = parent if parent.type in ('classdef', 'funcdef') else name
-        return get_cached_parent_scope(self._used_names, base_node) == self._parser_scope
+        return get_cached_parent_scope(self._parso_cache_node, base_node) == self._parser_scope
 
     def _check_flows(self, names):
         for name in sorted(names, key=lambda name: name.start_pos, reverse=True):
diff --git a/jedi/inference/value/klass.py b/jedi/inference/value/klass.py
index 071ec4d5..ee8d4e85 100644
--- a/jedi/inference/value/klass.py
+++ b/jedi/inference/value/klass.py
@@ -114,7 +114,7 @@ class ClassFilter(ParserTreeFilter):
         while node is not None:
             if node == self._parser_scope or node == self.parent_context:
                 return True
-            node = get_cached_parent_scope(self._used_names, node)
+            node = get_cached_parent_scope(self._parso_cache_node, node)
         return False
 
     def _access_possible(self, name):
diff --git a/jedi/parser_utils.py b/jedi/parser_utils.py
index 61f4d491..3c7fa151 100644
--- a/jedi/parser_utils.py
+++ b/jedi/parser_utils.py
@@ -216,11 +216,14 @@ def is_scope(node):
 def _get_parent_scope_cache(func):
     cache = WeakKeyDictionary()
 
-    def wrapper(used_names, node, include_flows=False):
+    def wrapper(parso_cache_node, node, include_flows=False):
+        if parso_cache_node is None:
+            return func(node, include_flows)
+
         try:
-            for_module = cache[used_names]
+            for_module = cache[parso_cache_node]
         except KeyError:
-            for_module = cache[used_names] = {}
+            for_module = cache[parso_cache_node] = {}
 
         try:
             return for_module[node]
@@ -274,6 +277,13 @@ def get_cached_code_lines(grammar, path):
 
 
 def get_parso_cache_node(grammar, path):
+    """
+    This is of course not public. But as long as I control parso, this
+    shouldn't be a problem. ~ Dave
+
+    The reason for this is mostly caching. This is obviously also a sign of a
+    broken caching architecture.
+    """
     return parser_cache[grammar._hashed][path]
 
 
diff --git a/test/test_parso_integration/test_parser_utils.py b/test/test_parso_integration/test_parser_utils.py
index 91f04c3f..d29bf751 100644
--- a/test/test_parso_integration/test_parser_utils.py
+++ b/test/test_parso_integration/test_parser_utils.py
@@ -84,8 +84,5 @@ def test_parser_cache_clear(Script):
     del parser_cache[script._inference_state.grammar._hashed][script.path]
     del script
 
-    import jedi
-    jedi.parser_utils.get_cached_parent_scope.__closure__[0].cell_contents.clear()
-
     gc.collect()
     assert module_id not in [id(m) for m in gc.get_referrers(tree.Module)]