diff --git a/libupower-glib/up-client.c b/libupower-glib/up-client.c
index 663f1c6..83b033b 100644
--- a/libupower-glib/up-client.c
+++ b/libupower-glib/up-client.c
@@ -106,7 +106,15 @@ up_client_get_devices_full (UpClient      *client,
 	GPtrArray *array;
 	guint i;
 
-	g_return_val_if_fail (UP_IS_CLIENT (client), NULL);
+	if (!UP_IS_CLIENT (client)) {
+		g_set_error (error, G_IO_ERROR,
+			     G_IO_ERROR_INVALID_ARGUMENT,
+			     "Invalid UpClient object");
+		g_return_if_fail_warning (G_LOG_DOMAIN,
+					  G_STRFUNC,
+					  "UP_IS_CLIENT (client)");
+		return NULL;
+	}
 
 	if (up_exported_daemon_call_enumerate_devices_sync (client->priv->proxy,
 							    &devices,