diff --git a/contrib/modsecurity/spoa.c b/contrib/modsecurity/spoa.c
index 81e3118..225db29 100644
--- a/contrib/modsecurity/spoa.c
+++ b/contrib/modsecurity/spoa.c
@@ -1374,7 +1374,8 @@
 	frame->flags  = 0;
 
 	ret = prepare_agentack(frame);
-	p = frame->buf + ret;
+	p   = frame->buf + ret;
+	end = frame->buf+max_frame_size;
 
 	if (frame->modsec_code != -1) {
 		DEBUG(frame->worker, "Add action : set variable code=%u",