diff --git a/locale.c b/locale.c
index abc17ee28379..a5a4ff29ba57 100644
--- a/locale.c
+++ b/locale.c
@@ -1812,6 +1812,7 @@ S_stdize_locale(pTHX_ const int category,
                           caller_line, category, input_locale));
 
     if (input_locale == NULL) {
+        SET_EINVAL;
         return NULL;
     }