diff -r 51057823b528 -r 3be141d6c82c cubicweb/server/migractions.py
--- a/cubicweb/server/migractions.py	Thu Jan 19 11:12:07 2017 +0100
+++ b/cubicweb/server/migractions.py	Thu Jan 19 11:12:35 2017 +0100
@@ -1133,7 +1133,8 @@
             schemaobj = getattr(rdef, attr)
             if getattr(schemaobj, 'eid', None) is None:
                 schemaobj.eid = self.repo.schema[schemaobj].eid
-                assert schemaobj.eid is not None, schemaobj
+                assert schemaobj.eid is not None, \
+                    '%s has no eid while adding %s' % (schemaobj, rdef)
         return rdef
 
     def cmd_drop_relation_definition(self, subjtype, rtype, objtype, commit=True):