diff --git a/include/curl/websockets.h b/include/curl/websockets.h
index d7387a1aec..fd6a916547 100644
--- a/include/curl/websockets.h
+++ b/include/curl/websockets.h
@@ -33,6 +33,7 @@ struct curl_ws_frame {
   int flags;            /* See the CURLWS_* defines */
   curl_off_t offset;    /* the offset of this data into the frame */
   curl_off_t bytesleft; /* number of pending bytes left of the payload */
+  size_t len;           /* size of the current data chunk */
 };
 
 /* flag bits */