diff --git a/python/google/protobuf/descriptor_pool.py b/python/google/protobuf/descriptor_pool.py
index b3df593f03..1f8ee12423 100644
--- a/python/google/protobuf/descriptor_pool.py
+++ b/python/google/protobuf/descriptor_pool.py
@@ -257,7 +257,7 @@ class DescriptorPool(object):
     self._AddFileDescriptor(file_desc)
     # TODO(jieluo): This is a temporary solution for FieldDescriptor.file.
     # Remove it when FieldDescriptor.file is added in code gen.
-    for extension in file_desc.extensions_by_name.itervalues():
+    for extension in file_desc.extensions_by_name.items():
       self._file_desc_by_toplevel_extension[
           extension.full_name] = file_desc