MappingView is Sized.
diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
index c241a95..cc4c442 100644
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -382,7 +382,7 @@
         return not (self == other)
 
 
-class MappingView(metaclass=ABCMeta):
+class MappingView(Sized):
 
     def __init__(self, mapping):
         self._mapping = mapping