diff --git a/net/caif/cfrfml.c b/net/caif/cfrfml.c
index 81660f809713..6dc75d4f8d94 100644
--- a/net/caif/cfrfml.c
+++ b/net/caif/cfrfml.c
@@ -190,7 +190,7 @@ out:
 
 static int cfrfml_transmit_segment(struct cfrfml *rfml, struct cfpkt *pkt)
 {
-	caif_assert(cfpkt_getlen(pkt) < rfml->fragment_size);
+	caif_assert(cfpkt_getlen(pkt) < rfml->fragment_size + RFM_HEAD_SIZE);
 
 	/* Add info for MUX-layer to route the packet out. */
 	cfpkt_info(pkt)->channel_id = rfml->serv.layer.id;