diff --git a/src/mm-iface-modem-signal.c b/src/mm-iface-modem-signal.c
index 2a30d3a4..e3a0bb77 100644
--- a/src/mm-iface-modem-signal.c
+++ b/src/mm-iface-modem-signal.c
@@ -501,6 +501,9 @@ interface_initialization_step (GTask *task)
         g_task_return_boolean (task, TRUE);
         g_object_unref (task);
         return;
+
+    default:
+        break;
     }
 
     g_assert_not_reached ();