diff --git a/lib/url.c b/lib/url.c
index 3c5240b780273a5b9b12453f43a1c728cf3dff1c..2b8a09794dd046944fd3c0d9347b1fdb2493fb41 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -1177,7 +1177,8 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option, ...)
      */
     data->set.buffer_size = va_arg(param, long);
 
-    if(data->set.buffer_size> (BUFSIZE -1 ))
+    if((data->set.buffer_size> (BUFSIZE -1 )) ||
+       (data->set.buffer_size < 1))
       data->set.buffer_size = 0; /* huge internal default */
 
     break;