explicit typecast to visualize that we really want the result of the

operation as a size_t

lib/http.c

@@ -1259,7 +1259,7 @@ CURLcode Curl_http(struct connectdata *conn)
          input. If we knew it was a proper file we could've just
          fseek()ed but we only have a stream here */
       do {
-        size_t readthisamountnow = (conn->resume_from - passed);
+        size_t readthisamountnow = (size_t)(conn->resume_from - passed);
         size_t actuallyread;
 
         if(readthisamountnow > BUFSIZE)