diff --git a/lib/http.c b/lib/http.c
index e0d3cda9bfb0fb30167d48b79210061a124a82f7..c4d44b47c518e0c48fe7c19573941f7190793b22 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -151,7 +151,7 @@ CURLcode add_buffer_send(int sockfd, struct connectdata *conn, send_buffer *in,
       break;
 
     if(amount != size) {
-      size += amount;
+      size -= amount;
       ptr += amount;
     }
     else