diff --git a/tests/perf/perf_fast_forward.cc b/tests/perf/perf_fast_forward.cc
index 2b6993dfef..30bfde1257 100644
--- a/tests/perf/perf_fast_forward.cc
+++ b/tests/perf/perf_fast_forward.cc
@@ -350,7 +350,7 @@ public:
 
         const std::string test_run_count_name = "test_run_count";
         params_value[test_run_count_name.c_str()] = test_run_count;
-        params_value[all_params_names + "," + test_run_count_name] = all_params_values + sprint(",%d", test_run_count);
+        params_value[all_params_names + "," + test_run_count_name] = all_params_values + std::string(sprint(",%d", test_run_count));
 
         Json::Value stats_value{Json::objectValue};
         for (size_t i = 0; i < stats_names.size(); ++i) {