diff --git a/src/xcl/xcblock.c b/src/xcl/xcblock.c
index 5a057241..1a5eb4f8 100644
--- a/src/xcl/xcblock.c
+++ b/src/xcl/xcblock.c
@@ -207,7 +207,9 @@ static inline int issue_complete_request(Display *dpy, int veclen, struct iovec
 	flags |= XCB_REQUEST_CHECKED;
 
     /* send the accumulated request. */
-    XCBSendRequest(dpy->xcl->connection, &sequence, flags, vec, &xcb_req);
+    sequence = XCBSendRequest(dpy->xcl->connection, flags, vec, &xcb_req);
+    if(!sequence)
+	_XIOError(dpy);
 
     /* update the iovecs to refer only to data not yet sent. */
     vec[i].iov_len = -len;