diff --git a/libcxx/src/support/win32/locale_win32.cpp b/libcxx/src/support/win32/locale_win32.cpp
--- a/libcxx/src/support/win32/locale_win32.cpp
+++ b/libcxx/src/support/win32/locale_win32.cpp
@@ -96,11 +96,15 @@
         _CRT_INTERNAL_LOCAL_PRINTF_OPTIONS | _CRT_INTERNAL_PRINTF_STANDARD_SNPRINTF_BEHAVIOR,
         ret, n, format, loc, ap);
 #else
-    __libcpp_locale_guard __current(loc);
-    _LIBCPP_DIAGNOSTIC_PUSH
-    _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wformat-nonliteral")
-    int result = vsnprintf( ret, n, format, ap );
-    _LIBCPP_DIAGNOSTIC_POP
+    int result;
+    if (n != 0) {
+      va_list ap_copy;
+      va_copy(ap_copy, ap);
+      result = _vsnprintf_s_l(ret, n, _TRUNCATE, format, loc, ap_copy);
+      va_end(ap_copy);
+    }
+    if (n == 0 || result < 0)
+      result = _vscprintf_l(format, loc, ap);
 #endif
     va_end(ap);
     return result;