diff --git a/src/gb/gprs_bssgp.c b/src/gb/gprs_bssgp.c
index 14a5e9d..c967f73 100644
--- a/src/gb/gprs_bssgp.c
+++ b/src/gb/gprs_bssgp.c
@@ -77,6 +77,7 @@
 /* callback to be backward compatible with old users which do not set the bssgp_ns_send function */
 static int _gprs_ns_sendmsg(void *ctx, struct msgb *msg)
 {
+	OSMO_ASSERT(bssgp_nsi);
 	return gprs_ns_sendmsg(bssgp_nsi, msg);
 }