diff --git a/src/c_api/c_api_symbolic.cc b/src/c_api/c_api_symbolic.cc
index a847b7409f6b..31816a71987e 100644
--- a/src/c_api/c_api_symbolic.cc
+++ b/src/c_api/c_api_symbolic.cc
@@ -1402,17 +1402,17 @@ int MXOptimizeForBackend(SymbolHandle sym_handle,
 
       // create the input shape, dtype and stype maps
       std::unordered_map<std::string, mxnet::TShape> input_shape_map(num_input_shapes);
-      for (int i = 0; i < num_input_shapes; ++i) {
+      for (uint32_t i = 0; i < num_input_shapes; ++i) {
         input_shape_map.emplace(input_shape_names[i],
                     mxnet::TShape(input_shape_data + input_shape_idx[i],
                     input_shape_data + input_shape_idx[i+1]));
       }
       std::unordered_map<std::string, int> input_dtype_map(num_input_dtypes);
-      for (int i = 0; i < num_input_dtypes; ++i) {
+      for (uint32_t i = 0; i < num_input_dtypes; ++i) {
         input_dtype_map.emplace(input_dtype_names[i], input_dtypes[i]);
       }
       std::unordered_map<std::string, int> input_stype_map(num_input_stypes);
-      for (int i = 0; i < num_input_stypes; ++i) {
+      for (uint32_t i = 0; i < num_input_stypes; ++i) {
         input_stype_map.emplace(input_stype_names[i], input_stypes[i]);
       }