diff --git a/calsocial/forms.py b/calsocial/forms.py
index 91e10fa..a93504b 100644
--- a/calsocial/forms.py
+++ b/calsocial/forms.py
@@ -52,7 +52,7 @@ class TimezoneField(SelectField):
 
             return
 
-        if is_pytz_instance(value):
+        if self.is_pytz_instance(value):
             self.data = value
 
             return