diff --git a/include/llvm/ADT/MapVector.h b/include/llvm/ADT/MapVector.h
index 3f7a5964138..6aacca5a6f0 100644
--- a/include/llvm/ADT/MapVector.h
+++ b/include/llvm/ADT/MapVector.h
@@ -78,6 +78,11 @@ public:
     }
     return Vector[I].second;
   }
+
+  unsigned count(const KeyT &Key) const {
+    typename MapType::const_iterator Pos = Map.find(Key);
+    return Pos == Map.end()? 0 : 1;
+  }
 };
 
 }