diff --git a/DataStructures/BinaryHeap.h b/DataStructures/BinaryHeap.h
index 5bbcb3b3f..6b9bd10c4 100644
--- a/DataStructures/BinaryHeap.h
+++ b/DataStructures/BinaryHeap.h
@@ -186,8 +186,8 @@ public:
 
     void DecreaseKey( NodeID node, Weight weight ) {
         assert( UINT_MAX != node );
-        const Key index = nodeIndex[node];
-        Key key = insertedNodes[index].key;
+        const Key & index = nodeIndex[node];
+        Key & key = insertedNodes[index].key;
         assert ( key >= 0 );
 
         insertedNodes[index].weight = weight;