diff --git a/calsocial/forms.py b/calsocial/forms.py
index 6d6e631..e7adf73 100644
--- a/calsocial/forms.py
+++ b/calsocial/forms.py
@@ -17,6 +17,8 @@
 """Forms for Calendar.social
 """
 
+from enum import Enum
+
 from flask_babelex import lazy_gettext as _
 from flask_security.forms import LoginForm as BaseLoginForm
 from flask_wtf import FlaskForm
@@ -173,6 +175,9 @@ class TimezoneField(SelectField):
 
 class EnumField(SelectField):
     def __init__(self, enum_type, translations, *args, **kwargs):
+        if not issubclass(enum_type, Enum):
+            raise TypeError('enum_type must be a subclass of Enum')
+
         kwargs.update({'choices': [(value, None) for value in enum_type]})
         self.data = None
         self.enum_type = enum_type