diff --git a/flask_simpleldap/__init__.py b/flask_simpleldap/__init__.py
index 82ae17fcd2326e51a2617ac8a7ca485cf5274ef6..abeb4181bfdacbcc10116767a4323ca76b07403d 100644
--- a/flask_simpleldap/__init__.py
+++ b/flask_simpleldap/__init__.py
@@ -150,7 +150,9 @@ class LDAP(object):
             return
         try:
             conn = self.initialize
-            conn.simple_bind_s(user_dn.decode('utf-8'), password)
+            _user_dn = user_dn.decode('utf-8') \
+                if isinstance(user_dn, bytes) else user_dn
+            conn.simple_bind_s(_user_dn, password)
             return True
         except ldap.LDAPError:
             return