diff --git a/utility.hpp b/utility.hpp
index c1a787a..0c9ee9c 100644
--- a/utility.hpp
+++ b/utility.hpp
@@ -339,12 +339,14 @@ namespace SimpleWeb {
       auto time = std::chrono::system_clock::to_time_t(time_point);
       tm tm;
 #ifdef _MSC_VER
-      auto gmtime = gmtime_s(&time, &tm);
+      if(gmtime_s(&tm, &time) != 0)
+        return {};
+      auto gmtime = &tm;
 #else
       auto gmtime = gmtime_r(&time, &tm);
-#endif
       if(!gmtime)
         return {};
+#endif
 
       switch(gmtime->tm_wday) {
       case 0: result += "Sun, "; break;