1 files changed, 4 insertions, 1 deletions
diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index f0b41fd..9a753db 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -920,7 +920,10 @@ class ChainMap(_collections_abc.MutableMapping):
         return len(set().union(*self.maps))     # reuses stored hash values if possible
 
     def __iter__(self):
-        return iter(set().union(*self.maps))
+        d = {}
+        for mapping in reversed(self.maps):
+            d.update(mapping)                   # reuses stored hash values if possible
+        return iter(d)
 
     def __contains__(self, key):
         return any(key in m for m in self.maps)