diff --git a/mace/ops/concat_test.cc b/mace/ops/concat_test.cc
index 6d376c62538ec7490d1db361c398f1078f4a70c5..216d3413bd7a46431843b9ca4149b7b2900ea913 100644
--- a/mace/ops/concat_test.cc
+++ b/mace/ops/concat_test.cc
@@ -97,7 +97,7 @@ TEST_F(ConcatOpTest, Random) {
   auto &net = test_net();
   auto builder = OpDefBuilder("Concat", "ConcatTest");
   for (int i = 0; i < num_inputs; ++i) {
-    builder = builder.Input(("Input" + std::to_string(i)).c_str());
+    builder = builder.Input(("Input" + ToString(i)).c_str());
   }
   builder.Input("Axis")
       .Output("Output")
@@ -114,7 +114,7 @@ TEST_F(ConcatOpTest, Random) {
     concat_axis_size += input_shapes[i][axis];
     GenerateRandomRealTypeData(input_shapes[i], inputs[i]);
     input_ptrs[i] = inputs[i].data();
-    net.AddInputFromArray<float>(("Input" + std::to_string(i)).c_str(), input_shapes[i], inputs[i]);
+    net.AddInputFromArray<float>(("Input" + ToString(i)).c_str(), input_shapes[i], inputs[i]);
   }
   net.AddInputFromArray<int>("Axis", {}, {axis});
 
diff --git a/mace/ops/ops_test_util.h b/mace/ops/ops_test_util.h
index ed6516874a5076d5c2012d1a0ef50bf3dd4cabd1..68ba9feae97b0efaa9f60dc3aee80013b7be340a 100644
--- a/mace/ops/ops_test_util.h
+++ b/mace/ops/ops_test_util.h
@@ -302,6 +302,13 @@ void ExpectTensorNear(const Tensor &x, const Tensor &y, const double abs_err) {
   Expector<T>::Near(x, y, abs_err);
 }
 
+template<typename T>
+std::string ToString(const T& input) {
+  std::stringstream ss;
+  ss<<input;
+  return ss.str();
+}
+
 }  // namespace mace
 
 #endif  //  MACE_OPS_TEST_UTIL_H_