diff --git a/src/wps/wps_upnp.c b/src/wps/wps_upnp.c
index f62b49e60..ae94a9f62 100644
--- a/src/wps/wps_upnp.c
+++ b/src/wps/wps_upnp.c
@@ -596,7 +596,10 @@ static struct wpabuf * build_fake_wsc_ack(void)
 	wpabuf_put_be16(msg, ATTR_REGISTRAR_NONCE);
 	wpabuf_put_be16(msg, WPS_NONCE_LEN);
 	wpabuf_put(msg, WPS_NONCE_LEN);
-	wps_build_wfa_ext(msg, 0, NULL, 0);
+	if (wps_build_wfa_ext(msg, 0, NULL, 0)) {
+		wpabuf_free(msg);
+		return NULL;
+	}
 	return msg;
 }