diff --git a/src/catch2/catch_tostring.hpp b/src/catch2/catch_tostring.hpp
index b718a18b..2fd613d3 100644
--- a/src/catch2/catch_tostring.hpp
+++ b/src/catch2/catch_tostring.hpp
@@ -558,27 +558,27 @@ struct ratio_string {
 
 template <>
 struct ratio_string<std::atto> {
-    static std::string symbol() { return "a"; }
+    static char symbol() { return 'a'; }
 };
 template <>
 struct ratio_string<std::femto> {
-    static std::string symbol() { return "f"; }
+    static char symbol() { return 'f'; }
 };
 template <>
 struct ratio_string<std::pico> {
-    static std::string symbol() { return "p"; }
+    static char symbol() { return 'p'; }
 };
 template <>
 struct ratio_string<std::nano> {
-    static std::string symbol() { return "n"; }
+    static char symbol() { return 'n'; }
 };
 template <>
 struct ratio_string<std::micro> {
-    static std::string symbol() { return "u"; }
+    static char symbol() { return 'u'; }
 };
 template <>
 struct ratio_string<std::milli> {
-    static std::string symbol() { return "m"; }
+    static char symbol() { return 'm'; }
 };
 
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