diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
index bf1417d..93fb5b5 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
@@ -635,8 +635,10 @@
 		return NULL;
 	}
 
-	if (*len < sizeof(struct gsm48_hdr)) {
-		LOGP(DNAT, LOGL_ERROR, "GSM48 header does not fit.\n");
+	if (msgb_l3len(msg) - 3 < msg->l3h[2]) {
+		LOGP(DNAT, LOGL_ERROR,
+		     "GSM48 payload does not fit: %d %d\n",
+		     msg->l3h[2], msgb_l3len(msg) - 3);
 		return NULL;
 	}