diff --git a/gtk/gtkcalendar.c b/gtk/gtkcalendar.c
index cd6f687179..94233333d5 100644
--- a/gtk/gtkcalendar.c
+++ b/gtk/gtkcalendar.c
@@ -1273,6 +1273,9 @@ calendar_arrow_rectangle (GtkCalendar  *calendar,
         rect->x = (allocation.width - padding.left - padding.right
                    - 3 - priv->arrow_width);
       break;
+
+    default:
+      g_assert_not_reached ();
     }
 
   rect->x += padding.left;