diff --git a/src/mm-port-qmi.c b/src/mm-port-qmi.c
index 844075ea..a0fd131a 100644
--- a/src/mm-port-qmi.c
+++ b/src/mm-port-qmi.c
@@ -590,6 +590,9 @@ port_open_step (GTask *task)
         g_task_return_boolean (task, TRUE);
         g_object_unref (task);
         return;
+
+    default:
+        g_assert_not_reached ();
     }
 }