diff --git a/openbsc/include/openbsc/gsm_data_shared.h b/openbsc/include/openbsc/gsm_data_shared.h
index d88995970..487a3f397 100644
--- a/openbsc/include/openbsc/gsm_data_shared.h
+++ b/openbsc/include/openbsc/gsm_data_shared.h
@@ -46,6 +46,10 @@ enum gsm_chreq_reason_t {
 	GSM_CHREQ_REASON_OTHER,
 };
 
+/* lchans 0..3 are SDCCH in combined channel configuration,
+   use 4 as magic number for BCCH hack - see osmo-bts-../oml.c:opstart_compl() */
+#define CCCH_LCHAN 4
+
 #define TRX_NR_TS	8
 #define TS_MAX_LCHAN	8
 
diff --git a/openbsc/src/libcommon/gsm_data_shared.c b/openbsc/src/libcommon/gsm_data_shared.c
index b8853ad69..df204feab 100644
--- a/openbsc/src/libcommon/gsm_data_shared.c
+++ b/openbsc/src/libcommon/gsm_data_shared.c
@@ -579,7 +579,7 @@ uint8_t gsm_pchan2chan_nr(enum gsm_phys_chan_config pchan,
 		 * here. This should never be sent in an RSL message.
 		 * See osmo-bts-xxx/oml.c:opstart_compl().
 		 */
-		if (lchan_nr == 4)
+		if (lchan_nr == CCCH_LCHAN)
 			chan_nr = 0;
 		else
 			OSMO_ASSERT(lchan_nr < 4);