diff --git a/contrib/mod_defender/spoa.c b/contrib/mod_defender/spoa.c
index d2b333ce4..94e6d6bda 100644
--- a/contrib/mod_defender/spoa.c
+++ b/contrib/mod_defender/spoa.c
@@ -1345,7 +1345,8 @@ process_frame_cb(evutil_socket_t fd, short events, void *arg)
 	frame->flags  = 0;
 
 	ret = prepare_agentack(frame);
-	p = frame->buf + ret;
+	p   = frame->buf + ret;
+	end = frame->buf+max_frame_size;
 
 	if (frame->defender_status != -1) {
 		DEBUG(frame->worker, "Add action : set variable status=%u",