diff --git a/call.py b/call.py
index fb4eb5f..162970f 100644
--- a/call.py
+++ b/call.py
@@ -77,7 +77,8 @@ class PendingTask(ModelSQL, ModelView):
         super(PendingTask, cls).__setup__()
         cls._buttons.update({
             'close_task': {
-                'invisible': Eval('state') == 'done'
+                'invisible': Eval('state') == 'done',
+                'depends': ['state'],
                 }
             })