diff --git a/lib/http.c b/lib/http.c
index 19473d3f1957cbc72461eb7156a39828cb69ef70..3aa5af34af3b9a6cacb37656692b2723d1f00928 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -1487,7 +1487,7 @@ CURLcode Curl_http(struct connectdata *conn)
       if(!conn->bits.upload_chunky)
         /* only add Content-Length if not uploading chunked */
         add_bufferf(req_buffer,
-                    "Content-Length: %d\r\n", http->postsize);
+                    "Content-Length: %" FORMAT_OFF_T "\r\n", http->postsize);
 
       if(!checkheaders(data, "Expect:")) {
         /* if not disabled explicitly we add a Expect: 100-continue