diff --git a/src/compositor/meta-background.c b/src/compositor/meta-background.c
index 0fb784a15..0370f5515 100644
--- a/src/compositor/meta-background.c
+++ b/src/compositor/meta-background.c
@@ -133,8 +133,13 @@ on_monitors_changed (MetaScreen     *screen,
 
   if (priv->screen)
     {
+      int i;
+
       priv->n_monitors = meta_screen_get_n_monitors (screen);
       priv->monitors = g_new0 (MetaBackgroundMonitor, priv->n_monitors);
+
+      for (i = 0; i < priv->n_monitors; i++)
+        priv->monitors[i].dirty = TRUE;
     }
 }