diff --git a/examples/client_test.cpp b/examples/client_test.cpp
index 56ad71b02..09769f847 100644
--- a/examples/client_test.cpp
+++ b/examples/client_test.cpp
@@ -186,9 +186,16 @@ std::string to_string(int v, int width)
 	return s.str();
 }
 
-std::string const& to_string(float v, int width, int precision = 3)
+std::string& to_string(float v, int width, int precision = 3)
 {
-	static std::string ret;
+	// this is a silly optimization
+	// to avoid copying of strings
+	enum { num_strings = 20 };
+	static std::string buf[num_strings];
+	static int round_robin = 0;
+	std::string& ret = buf[round_robin];
+	++round_robin;
+	if (round_robin >= num_strings) round_robin = 0;
 	ret.resize(20);
 	int size = std::sprintf(&ret[0], "%*.*f", width, precision, v);
 	ret.resize((std::min)(size, width));
@@ -229,7 +236,6 @@ std::string ratio(float a, float b)
 
 std::string const& add_suffix(float val)
 {
-	static std::string ret;
 	const char* prefix[] = {"kB", "MB", "GB", "TB"};
 	const int num_prefix = sizeof(prefix) / sizeof(const char*);
 	for (int i = 0; i < num_prefix; ++i)
@@ -237,12 +243,12 @@ std::string const& add_suffix(float val)
 		val /= 1000.f;
 		if (fabs(val) < 1000.f)
 		{
-			ret = to_string(val, 4);
+			std::string& ret = to_string(val, 4);
 			ret += prefix[i];
 			return ret;
 		}
 	}
-	ret = to_string(val, 4);
+	std::string& ret = to_string(val, 4);
 	ret += "PB";
 	return ret;
 }