diff --git a/openbsc/src/libcommon/gsm_data.c b/openbsc/src/libcommon/gsm_data.c
index b1fb4db..a85eb84 100644
--- a/openbsc/src/libcommon/gsm_data.c
+++ b/openbsc/src/libcommon/gsm_data.c
@@ -156,6 +156,7 @@
 		ts->trx = trx;
 		ts->nr = k;
 		ts->pchan = GSM_PCHAN_NONE;
+		ts->tsc = -1;
 
 		ts->hopping.arfcns.data_len = sizeof(ts->hopping.arfcns_data);
 		ts->hopping.arfcns.data = ts->hopping.arfcns_data;