diff --git a/openbsc/include/openbsc/bsc_api.h b/openbsc/include/openbsc/bsc_api.h
index a3d12f2..d0a0164 100644
--- a/openbsc/include/openbsc/bsc_api.h
+++ b/openbsc/include/openbsc/bsc_api.h
@@ -3,6 +3,8 @@
 #ifndef OPENBSC_BSC_API_H
 #define OPENBSC_BSC_API_H
 
+#include <stdbool.h>
+
 #include "gsm_data.h"
 
 #define BSC_API_CONN_POL_ACCEPT	0
@@ -45,7 +47,7 @@ struct bsc_api {
 
 int bsc_api_init(struct gsm_network *network, struct bsc_api *api);
 int gsm0808_submit_dtap(struct gsm_subscriber_connection *conn, struct msgb *msg, int link_id, int allow_sacch);
-int gsm0808_assign_req(struct gsm_subscriber_connection *conn, int chan_mode, int full_rate);
+int gsm0808_assign_req(struct gsm_subscriber_connection *conn, enum gsm48_chan_mode chan_mode, bool full_rate);
 int gsm0808_cipher_mode(struct gsm_subscriber_connection *conn, int cipher,
 			const uint8_t *key, int len, int include_imeisv);
 int gsm0808_page(struct gsm_bts *bts, unsigned int page_group,
diff --git a/openbsc/include/openbsc/gsm_04_08.h b/openbsc/include/openbsc/gsm_04_08.h
index fd0b89d..d333e13 100644
--- a/openbsc/include/openbsc/gsm_04_08.h
+++ b/openbsc/include/openbsc/gsm_04_08.h
@@ -79,7 +79,7 @@ int gsm48_extract_mi(uint8_t *classmark2, int length, char *mi_string, uint8_t *
 int gsm48_paging_extract_mi(struct gsm48_pag_resp *pag, int length, char *mi_string, uint8_t *mi_type);
 int gsm48_handle_paging_resp(struct gsm_subscriber_connection *conn, struct msgb *msg, struct gsm_subscriber *subscr);
 
-int gsm48_lchan_modify(struct gsm_lchan *lchan, uint8_t lchan_mode);
+int gsm48_lchan_modify(struct gsm_lchan *lchan, enum gsm48_chan_mode lchan_mode);
 int gsm48_rx_rr_modif_ack(struct msgb *msg);
 int gsm48_parse_meas_rep(struct gsm_meas_rep *rep, struct msgb *msg);
 
diff --git a/openbsc/include/openbsc/mncc.h b/openbsc/include/openbsc/mncc.h
index 49f0c8b..ce2f87d 100644
--- a/openbsc/include/openbsc/mncc.h
+++ b/openbsc/include/openbsc/mncc.h
@@ -26,6 +26,8 @@
 
 #include <osmocom/core/linuxlist.h>
 #include <osmocom/gsm/mncc.h>
+#include <osmocom/gsm/gsm_utils.h>
+#include <osmocom/gsm/protocol/gsm_04_08.h>
 
 #include <stdint.h>
 
@@ -156,8 +158,8 @@ struct gsm_mncc {
 	int		emergency;
 	char		imsi[16];
 
-	unsigned char	lchan_type;
-	unsigned char	lchan_mode;
+	enum gsm_chan_t lchan_type;
+	enum gsm48_chan_mode lchan_mode;
 };
 
 struct gsm_data_frame {
diff --git a/openbsc/include/openbsc/mncc_int.h b/openbsc/include/openbsc/mncc_int.h
index 213ce14..dafef25 100644
--- a/openbsc/include/openbsc/mncc_int.h
+++ b/openbsc/include/openbsc/mncc_int.h
@@ -3,12 +3,15 @@
 
 #include <stdint.h>
 
+#include <osmocom/gsm/gsm_utils.h>
+#include <osmocom/gsm/protocol/gsm_04_08.h>
+
 struct mncc_int {
 	uint8_t def_codec[2];
 };
 
 extern struct mncc_int mncc_int;
 
-uint8_t mncc_codec_for_mode(int lchan_type);
+enum gsm48_chan_mode mncc_codec_for_mode(enum gsm_chan_t lchan_type);
 
 #endif
diff --git a/openbsc/src/libbsc/bsc_api.c b/openbsc/src/libbsc/bsc_api.c
index e6d820d..9ddd647 100644
--- a/openbsc/src/libbsc/bsc_api.c
+++ b/openbsc/src/libbsc/bsc_api.c
@@ -21,6 +21,8 @@
  *
  */
 
+#include <stdbool.h>
+
 #include <openbsc/bsc_api.h>
 #include <openbsc/bsc_rll.h>
 #include <openbsc/gsm_data.h>
@@ -34,7 +36,7 @@
 #include <openbsc/trau_mux.h>
 
 #include <osmocom/gsm/protocol/gsm_08_08.h>
-
+#include <osmocom/gsm/protocol/gsm_04_08.h>
 #include <osmocom/core/talloc.h>
 
 #define GSM0808_T10_VALUE    6, 0
@@ -155,7 +157,7 @@ static void assignment_t10_timeout(void *_conn)
  * Handle the multirate config
  */
 static void handle_mr_config(struct gsm_subscriber_connection *conn,
-			     struct gsm_lchan *lchan, int full_rate)
+			     struct gsm_lchan *lchan, bool full_rate)
 {
 	struct bsc_api *api;
 	api = conn->bts->network->bsc_api;
@@ -197,12 +199,10 @@ static void handle_mr_config(struct gsm_subscriber_connection *conn,
  * -> Assignment Complete/Assignment Failure
  *  5.) Release the SDCCH, continue signalling on the new link
  */
-static int handle_new_assignment(struct gsm_subscriber_connection *conn, int chan_mode, int full_rate)
+static int handle_new_assignment(struct gsm_subscriber_connection *conn, enum gsm48_chan_mode chan_mode, bool full_rate)
 {
 	struct gsm_lchan *new_lchan;
-	int chan_type;
-
-	chan_type = full_rate ? GSM_LCHAN_TCH_F : GSM_LCHAN_TCH_H;
+	enum gsm_chan_t chan_type = full_rate ? GSM_LCHAN_TCH_F : GSM_LCHAN_TCH_H;
 
 	new_lchan = lchan_alloc(conn->bts, chan_type, 0);
 
@@ -337,7 +337,7 @@ int gsm0808_submit_dtap(struct gsm_subscriber_connection *conn,
 /*
  * \brief Check if the given channel is compatible with the mode/fullrate
  */
-static int chan_compat_with_mode(struct gsm_lchan *lchan, int chan_mode, int full_rate)
+static int chan_compat_with_mode(struct gsm_lchan *lchan, enum gsm48_chan_mode chan_mode, bool full_rate)
 {
 	switch (chan_mode) {
 	case GSM48_CMODE_SIGN:
@@ -384,7 +384,8 @@ static int chan_compat_with_mode(struct gsm_lchan *lchan, int chan_mode, int ful
  *
  * TODO: Add multirate configuration, make it work for more than audio.
  */
-int gsm0808_assign_req(struct gsm_subscriber_connection *conn, int chan_mode, int full_rate)
+int gsm0808_assign_req(struct gsm_subscriber_connection *conn,
+		       enum gsm48_chan_mode chan_mode, bool full_rate)
 {
 	struct bsc_api *api;
 	api = conn->bts->network->bsc_api;
diff --git a/openbsc/src/libbsc/gsm_04_08_utils.c b/openbsc/src/libbsc/gsm_04_08_utils.c
index 8c6dbef..79a8547 100644
--- a/openbsc/src/libbsc/gsm_04_08_utils.c
+++ b/openbsc/src/libbsc/gsm_04_08_utils.c
@@ -488,7 +488,7 @@ int gsm48_send_rr_ass_cmd(struct gsm_lchan *dest_lchan, struct gsm_lchan *lchan,
 }
 
 /* 9.1.5 Channel mode modify: Modify the mode on the MS side */
-int gsm48_tx_chan_mode_modify(struct gsm_lchan *lchan, uint8_t mode)
+int gsm48_tx_chan_mode_modify(struct gsm_lchan *lchan, enum gsm48_chan_mode mode)
 {
 	struct msgb *msg = gsm48_msgb_alloc_name("GSM 04.08 CHN MOD");
 	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
@@ -513,15 +513,9 @@ int gsm48_tx_chan_mode_modify(struct gsm_lchan *lchan, uint8_t mode)
 	return gsm48_sendmsg(msg);
 }
 
-int gsm48_lchan_modify(struct gsm_lchan *lchan, uint8_t lchan_mode)
+int gsm48_lchan_modify(struct gsm_lchan *lchan, enum gsm48_chan_mode lchan_mode)
 {
-	int rc;
-
-	rc = gsm48_tx_chan_mode_modify(lchan, lchan_mode);
-	if (rc < 0)
-		return rc;
-
-	return rc;
+	return gsm48_tx_chan_mode_modify(lchan, lchan_mode);
 }
 
 int gsm48_rx_rr_modif_ack(struct msgb *msg)
diff --git a/openbsc/src/libmsc/mncc_builtin.c b/openbsc/src/libmsc/mncc_builtin.c
index 77df6fb..0942304 100644
--- a/openbsc/src/libmsc/mncc_builtin.c
+++ b/openbsc/src/libmsc/mncc_builtin.c
@@ -27,6 +27,9 @@
 #include <string.h>
 #include <errno.h>
 
+#include <osmocom/gsm/gsm_utils.h>
+#include <osmocom/gsm/protocol/gsm_04_08.h>
+
 #include <openbsc/gsm_04_08.h>
 #include <openbsc/debug.h>
 #include <openbsc/mncc.h>
@@ -65,7 +68,7 @@ static struct gsm_call *get_call_ref(uint32_t callref)
 	return NULL;
 }
 
-uint8_t mncc_codec_for_mode(int lchan_type)
+enum gsm48_chan_mode mncc_codec_for_mode(enum gsm_chan_t lchan_type)
 {
 	/* FIXME: check codec capabilities of the phone */
 
@@ -75,7 +78,7 @@ uint8_t mncc_codec_for_mode(int lchan_type)
 		return mncc_int.def_codec[1];
 }
 
-static uint8_t determine_lchan_mode(struct gsm_mncc *setup)
+static enum gsm48_chan_mode determine_lchan_mode(struct gsm_mncc *setup)
 {
 	return mncc_codec_for_mode(setup->lchan_type);
 }
