diff --git a/include/spdlog/common.h b/include/spdlog/common.h
index 465e848a..d2b39b7a 100644
--- a/include/spdlog/common.h
+++ b/include/spdlog/common.h
@@ -143,11 +143,11 @@ struct format_string_wrapper
         : fmt_{fmt}
         , loc_{loc}
     {}
-    SPDLOG_CONSTEXPR const T fmt()
+    SPDLOG_CONSTEXPR T fmt() const
     {
         return fmt_;
     }
-    SPDLOG_CONSTEXPR const source_loc loc()
+    SPDLOG_CONSTEXPR source_loc loc() const
     {
         return source_loc{loc_.file_name(), loc_.line(), loc_.function_name()};
     }