diff --git a/nnvm/src/top/op_common.h b/nnvm/src/top/op_common.h
index ee6b7ced3b4e71451c96aa589927643dc51eb5bb..ae4388ade1c01b3c25b63a227791bf4bc219f843 100644
--- a/nnvm/src/top/op_common.h
+++ b/nnvm/src/top/op_common.h
@@ -293,7 +293,7 @@ inline std::vector<NodeEntry> MakeGradNode(
   const char* op_name,
   const NodePtr& n,
   std::vector<NodeEntry> inputs,
-  std::unordered_map<std::string, std::string> attr = {}) {
+  std::unordered_map<std::string, std::string> attr = {{}}) {
   NodePtr p = Node::Create();
   p->attrs.op = nnvm::Op::Get(op_name);
   p->attrs.name = n->attrs.name + "_grad";