diff --git a/src/google/protobuf/map.h b/src/google/protobuf/map.h
index a9b933c..6c1d57f 100644
--- a/src/google/protobuf/map.h
+++ b/src/google/protobuf/map.h
@@ -364,7 +364,6 @@
     std::swap(index_of_first_non_null_, other->index_of_first_non_null_);
     std::swap(type_info_, other->type_info_);
     std::swap(table_, other->table_);
-    std::swap(arena_, other->arena_);
   }
 
   void UntypedMergeFrom(const UntypedMapBase& other);