diff --git a/openbsc/src/libcommon/gsm_subscriber_base.c b/openbsc/src/libcommon/gsm_subscriber_base.c
index a455824..50f4118 100644
--- a/openbsc/src/libcommon/gsm_subscriber_base.c
+++ b/openbsc/src/libcommon/gsm_subscriber_base.c
@@ -112,7 +112,7 @@
 	if (!subscr)
 		return NULL;
 
-	strncpy(subscr->imsi, imsi, GSM_IMSI_LENGTH-1);
+	strncpy(subscr->imsi, imsi, sizeof(subscr->imsi)-1);
 	subscr->group = sgrp;
 	return subscr;
 }