diff --git a/radicale-auth-ldap/__init__.py b/radicale-auth-ldap/__init__.py
index c1e7597..beea2d0 100644
--- a/radicale-auth-ldap/__init__.py
+++ b/radicale-auth-ldap/__init__.py
@@ -103,7 +103,7 @@ class Auth(BaseAuth):
                 userAttributeValue = conn.response[0]['attributes'][userAttribute]
                 logger.debug("LDAP user DN: %s" % userDn)
 
-                if (not accessGroupFilter == None) and (not accessGroupAttribute == None):
+                if (not accessGroupFilter == "None") and (not accessGroupAttribute == "None"):
                     userMemberOf = conn.response[0]['attributes'][accessGroupAttribute]
 
                     userIsInAccessGroup = False