diff --git a/programs/cmd/builtins.c b/programs/cmd/builtins.c
index 33e96c19e2b978f13660b8b3d0db9f78ca64ffee..af58717ead2b02aa1011608dc7974a43f80954ad 100644
--- a/programs/cmd/builtins.c
+++ b/programs/cmd/builtins.c
@@ -2303,7 +2303,7 @@ BOOL WCMD_ask_confirm (WCHAR *message, BOOL showSureText, BOOL *optionAll) {
       WCMD_output_asis (endBkt);
       WCMD_ReadFile (GetStdHandle(STD_INPUT_HANDLE), answer,
                      sizeof(answer)/sizeof(WCHAR), &count, NULL);
-      answer[0] = toupper(answer[0]);
+      answer[0] = toupperW(answer[0]);
     }
 
     /* Return the answer */