diff --git a/src/gsm/auth_xor_2g.c b/src/gsm/auth_xor_2g.c
index 1a96b4a..367c79d 100644
--- a/src/gsm/auth_xor_2g.c
+++ b/src/gsm/auth_xor_2g.c
@@ -48,6 +48,8 @@
 {
 	uint8_t res1[16];
 
+	OSMO_ASSERT(aud->algo == OSMO_AUTH_ALG_XOR_2G);
+
 	if (aud->type != OSMO_AUTH_TYPE_GSM)
 		return -ENOTSUP;