diff --git a/lib/formdata.c b/lib/formdata.c
index 3128f495b1..46542b4329 100644
--- a/lib/formdata.c
+++ b/lib/formdata.c
@@ -254,7 +254,7 @@ CURLFORMcode FormAdd(struct curl_httppost **httppost,
       /* This is not array-state, get next option. This gets an 'int' with
          va_arg() because CURLformoption might be a smaller type than int and
          might cause compiler warnings and wrong behavior. */
-      option = va_arg(params, int);
+      option = (CURLformoption)va_arg(params, int);
       if(CURLFORM_END == option)
         break;
     }