diff --git a/prospect_trace.py b/prospect_trace.py
index 5265aed..4189c5d 100644
--- a/prospect_trace.py
+++ b/prospect_trace.py
@@ -47,7 +47,7 @@ class ProspectTrace(ModelSQL, ModelView):
 
     @fields.depends('pending_calls', 'state')
     def on_change_pending_calls(self):
-        if self.pending_calls:
+        if len(self.pending_calls) > 0:
             self.state = 'with_pending_calls'
 
     @fields.depends('prospect')