diff --git a/test/testsupport/perf_test.cc b/test/testsupport/perf_test.cc
index e8608cd..bb4491a 100644
--- a/test/testsupport/perf_test.cc
+++ b/test/testsupport/perf_test.cc
@@ -75,11 +75,14 @@
 void PrintResultMeanAndError(const std::string& measurement,
                              const std::string& modifier,
                              const std::string& trace,
-                             const std::string& mean_and_error,
+                             const double mean,
+                             const double error,
                              const std::string& units,
                              bool important) {
-  PrintResultsImpl(measurement, modifier, trace, mean_and_error,
-                   "{", "}", units, important);
+  std::ostringstream value_stream;
+  value_stream << '{' << mean << ',' << error << '}';
+  PrintResultsImpl(measurement, modifier, trace, value_stream.str(), "", "",
+                   units, important);
 }
 
 void PrintResultList(const std::string& measurement,
diff --git a/test/testsupport/perf_test.h b/test/testsupport/perf_test.h
index 95bbf65..02dd1f3 100644
--- a/test/testsupport/perf_test.h
+++ b/test/testsupport/perf_test.h
@@ -47,7 +47,8 @@
 void PrintResultMeanAndError(const std::string& measurement,
                              const std::string& modifier,
                              const std::string& trace,
-                             const std::string& mean_and_error,
+                             const double mean,
+                             const double error,
                              const std::string& units,
                              bool important);