diff --git a/canaille/ldaputils.py b/canaille/ldaputils.py
index 9e5be236..bf828f71 100644
--- a/canaille/ldaputils.py
+++ b/canaille/ldaputils.py
@@ -171,7 +171,12 @@ class LDAPObject:
                 if v and v[0] and self.attrs.get(k) != v
             }
             attributes = [
-                (ldap.MOD_REPLACE, k, [elt.encode("utf-8") for elt in v])
+                (ldap.MOD_REPLACE, k, [
+                    elt.encode("utf-8")
+                    if isinstance(elt, str)
+                    else elt
+                    for elt in v
+                ])
                 for k, v in mods.items()
             ]
             conn.modify_s(self.dn, attributes)
@@ -186,7 +191,13 @@ class LDAPObject:
                     mods[k] = v
 
             attributes = [
-                (k, [elt.encode("utf-8") for elt in v]) for k, v in mods.items()
+                (k, [
+                    elt.encode("utf-8")
+                    if isinstance(elt, str)
+                    else elt
+                    for elt in v
+                ])
+                for k, v in mods.items()
             ]
             conn.add_s(self.dn, attributes)