diff --git a/lib/formdata.c b/lib/formdata.c
index 7ad8a1fa3..160f51fbd 100644
--- a/lib/formdata.c
+++ b/lib/formdata.c
@@ -875,7 +875,7 @@ CURLcode Curl_getFormData(struct FormData **finalform,
   struct curl_httppost *file;
   CURLcode result = CURLE_OK;
 
-  size_t size =0;
+  curl_off_t size =0;
   char *boundary;
   char *fileboundary=NULL;
   struct curl_slist* curList;