diff --git a/paddle/gserver/layers/CostLayer.h b/paddle/gserver/layers/CostLayer.h
index 0ce72ef40a5ac23d20f485eb5b518186d1ec0686..0f655b48eea051c41ce17c0a41189b26188cc866 100644
--- a/paddle/gserver/layers/CostLayer.h
+++ b/paddle/gserver/layers/CostLayer.h
@@ -318,7 +318,9 @@ public:
 
   void forwardImp(Matrix& output, Argument& label, Matrix& cost) override;
 
-  void backwardImp(Matrix& outputValue, Argument& label, Matrix& outputGrad) {}
+  void backwardImp(Matrix& outputValue,
+                   Argument& label,
+                   Matrix& outputGrad) override {}
 };
 
 /**