--- a/cubicweb/misc/migration/3.23.0_Any.py	Tue Dec 17 21:21:55 2019 +0100
+++ b/cubicweb/misc/migration/3.23.0_Any.py	Thu Dec 19 08:13:22 2019 +0100
@@ -61,7 +61,7 @@
     rdef = cwrdef.yams_schema()
     cstr = rdef.constraint_by_eid(cwconstraint.eid)
     with cnx.deny_all_hooks_but():
-        cwconstraint.cw_set(value=unicode(cstr.serialize()))
+        cwconstraint.cw_set(value=str(cstr.serialize()))
     if cstr.type() not in ('BoundaryConstraint', 'IntervalBoundConstraint',
                            'StaticVocabularyConstraint'):
         # These cannot be translate into backend CHECK.