diff --git a/openbsc/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index 650d113..bf88e0a 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -385,7 +385,7 @@
 int bsc_check_ussd(struct sccp_connections *con, struct bsc_nat_parsed *parsed, struct msgb *msg);
 int bsc_close_ussd_connections(struct bsc_nat *nat);
 
-struct msgb *bsc_nat_rewrite_setup(struct bsc_nat *nat, struct msgb *msg, struct bsc_nat_parsed *, const char *imsi);
+struct msgb *bsc_nat_rewrite_msg(struct bsc_nat *nat, struct msgb *msg, struct bsc_nat_parsed *, const char *imsi);
 
 /** paging group handling */
 struct bsc_nat_paging_group *bsc_nat_paging_group_num(struct bsc_nat *nat, int group);
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index 8649f43..e0eb635 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -1040,7 +1040,7 @@
 					 * replace the msg and the parsed structure becomes
 					 * invalid.
 					 */
-					msg = bsc_nat_rewrite_setup(bsc->nat, msg, parsed, con->imsi);
+					msg = bsc_nat_rewrite_msg(bsc->nat, msg, parsed, con->imsi);
 					talloc_free(parsed);
 					parsed = NULL;
 				} else if (con->con_local == NAT_CON_END_USSD) {
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
index a7b0044..47eaabd 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
@@ -838,39 +838,19 @@
 /**
  * Rewrite non global numbers... according to rules based on the IMSI
  */
-struct msgb *bsc_nat_rewrite_setup(struct bsc_nat *nat, struct msgb *msg, struct bsc_nat_parsed *parsed, const char *imsi)
+static struct msgb *rewrite_setup(struct bsc_nat *nat, struct msgb *msg,
+				  struct bsc_nat_parsed *parsed, const char *imsi,
+				  struct gsm48_hdr *hdr48, const uint32_t len)
 {
 	struct tlv_parsed tp;
-	struct gsm48_hdr *hdr48;
-	uint32_t len;
-	uint8_t msg_type, proto;
 	unsigned int payload_len;
 	struct gsm_mncc_number called;
-	char *new_number = NULL;
 	struct msgb *out, *sccp;
+	char *new_number = NULL;
 	uint8_t *outptr;
 	const uint8_t *msgptr;
 	int sec_len;
 
-	if (!imsi || strlen(imsi) < 5)
-		return msg;
-
-	/* only care about DTAP messages */
-	if (parsed->bssap != BSSAP_MSG_DTAP)
-		return msg;
-	if (!parsed->dest_local_ref)
-		return msg;
-
-	hdr48 = bsc_unpack_dtap(parsed, msg, &len);
-	if (!hdr48)
-		return msg;
-
-	proto = hdr48->proto_discr & 0x0f;
-	msg_type = hdr48->msg_type & 0xbf;
-	if (proto != GSM48_PDISC_CC ||
-	    msg_type != GSM48_MT_CC_SETUP)
-		return msg;
-
 	/* decode and rewrite the message */
 	payload_len = len - sizeof(*hdr48);
 	tlv_parse(&tp, &gsm48_att_tlvdef, hdr48->data, payload_len, 0, 0);
@@ -957,6 +937,33 @@
 	return sccp;
 }
 
+struct msgb *bsc_nat_rewrite_msg(struct bsc_nat *nat, struct msgb *msg, struct bsc_nat_parsed *parsed, const char *imsi)
+{
+	struct gsm48_hdr *hdr48;
+	uint32_t len;
+	uint8_t msg_type, proto;
+
+	if (!imsi || strlen(imsi) < 5)
+		return msg;
+
+	/* only care about DTAP messages */
+	if (parsed->bssap != BSSAP_MSG_DTAP)
+		return msg;
+	if (!parsed->dest_local_ref)
+		return msg;
+
+	hdr48 = bsc_unpack_dtap(parsed, msg, &len);
+	if (!hdr48)
+		return msg;
+
+	proto = hdr48->proto_discr & 0x0f;
+	msg_type = hdr48->msg_type & 0xbf;
+
+	if (proto == GSM48_PDISC_CC && msg_type == GSM48_MT_CC_SETUP)
+		return rewrite_setup(nat, msg, parsed, imsi, hdr48, len);
+
+	return msg;
+}
 static void num_rewr_free_data(struct bsc_nat_num_rewr_entry *entry)
 {
 	regfree(&entry->msisdn_reg);
diff --git a/openbsc/tests/bsc-nat/bsc_nat_test.c b/openbsc/tests/bsc-nat/bsc_nat_test.c
index 32f4f72..c9432fe 100644
--- a/openbsc/tests/bsc-nat/bsc_nat_test.c
+++ b/openbsc/tests/bsc-nat/bsc_nat_test.c
@@ -865,7 +865,7 @@
 		abort();
 	}
 
-	out = bsc_nat_rewrite_setup(nat, msg, parsed, imsi);
+	out = bsc_nat_rewrite_msg(nat, msg, parsed, imsi);
 	if (msg != out) {
 		fprintf(stderr, "FAIL: The message should not have been changed\n");
 		abort();
@@ -891,7 +891,7 @@
 		abort();
 	}
 
-	out = bsc_nat_rewrite_setup(nat, msg, parsed, imsi);
+	out = bsc_nat_rewrite_msg(nat, msg, parsed, imsi);
 	if (!out) {
 		fprintf(stderr, "FAIL: A new message should be created.\n");
 		abort();
@@ -926,7 +926,7 @@
 		abort();
 	}
 
-	out = bsc_nat_rewrite_setup(nat, msg, parsed, imsi);
+	out = bsc_nat_rewrite_msg(nat, msg, parsed, imsi);
 	if (!out) {
 		fprintf(stderr, "FAIL: A new message should be created.\n");
 		abort();
@@ -961,7 +961,7 @@
 		abort();
 	}
 
-	out = bsc_nat_rewrite_setup(nat, msg, parsed, imsi);
+	out = bsc_nat_rewrite_msg(nat, msg, parsed, imsi);
 	if (out != msg) {
 		fprintf(stderr, "FAIL: The message should be unchanged.\n");
 		abort();