diff --git a/Lib/_collections_abc.py b/Lib/_collections_abc.py
index 60b471317ce97c..44d930a0dd6616 100644
--- a/Lib/_collections_abc.py
+++ b/Lib/_collections_abc.py
@@ -106,11 +106,11 @@ async def _ag(): yield
 ### ONE-TRICK PONIES ###
 
 def _check_methods(C, *methods):
-    mro = C.__mro__
+    mro_dicts = [B.__dict__ for B in C.__mro__]
     for method in methods:
-        for B in mro:
-            if method in B.__dict__:
-                if B.__dict__[method] is None:
+        for base_dict in mro_dicts:
+            if method in base_dict:
+                if base_dict[method] is None:
                     return NotImplemented
                 break
         else: