diff --git a/src/authentic2_auth_kerberos/backends.py b/src/authentic2_auth_kerberos/backends.py
index 9f94725..21c41e4 100644
--- a/src/authentic2_auth_kerberos/backends.py
+++ b/src/authentic2_auth_kerberos/backends.py
@@ -85,7 +85,8 @@ class A2LdapKerberosBackend(LDAPBackend):
                            block['principal_filter'])
             return
 
-        user_basedn = block.get('user_basedn') or block['basedn']
+        user_basedn = encoding.force_text(block.get('user_basedn') or block['basedn'])
+        principal_filter = encoding.force_text(block['principal_filter'])
         principal_filter = FilterFormatter().format(block['principal_filter'], username=username,
                                                     realm=realm)
         for conn in self.get_connections(block):