diff --git a/src/gsm/auth_core.c b/src/gsm/auth_core.c
index c2a13a5..d0c9f1c 100644
--- a/src/gsm/auth_core.c
+++ b/src/gsm/auth_core.c
@@ -72,11 +72,18 @@
 		      const uint8_t *_rand)
 {
 	struct osmo_auth_impl *impl = selected_auths[aud->algo];
+	int rc;
 
 	if (!impl)
 		return -ENOENT;
 
-	return impl->gen_vec(vec, aud, _rand);
+	rc = impl->gen_vec(vec, aud, _rand);
+	if (rc < 0)
+		return rc;
+
+	memcpy(vec->rand, _rand, sizeof(vec->rand));
+
+	return 0;
 }
 
 int osmo_auth_gen_vec_auts(struct osmo_auth_vector *vec,