--- a/hooks/syncschema.py	Tue Apr 01 14:46:55 2014 +0200
+++ b/hooks/syncschema.py	Tue Apr 01 18:09:46 2014 +0200
@@ -650,7 +650,11 @@
         rdef = self.rdef
         # in-place modification of in-memory schema first
         _set_modifiable_constraints(rdef)
-        rdef.constraints.remove(self.oldcstr)
+        if self.oldcstr in rdef.constraints:
+            rdef.constraints.remove(self.oldcstr)
+        else:
+            self.critical('constraint %s for rdef %s was missing or already removed',
+                          self.oldcstr, rdef)
         # then update database: alter the physical schema on size/unique
         # constraint changes
         syssource = session.cnxset.source('system')
@@ -1132,12 +1136,11 @@
         if self._cw.deleted_in_transaction(self.eidfrom):
             return
         schema = self._cw.vreg.schema
-        entity = self._cw.entity_from_eid(self.eidto)
         rdef = schema.schema_by_eid(self.eidfrom)
         try:
-            cstr = rdef.constraint_by_type(entity.type)
-        except IndexError:
-            self._cw.critical('constraint type no more accessible')
+            cstr = rdef.constraint_by_eid(self.eidto)
+        except ValueError:
+            self._cw.critical('constraint no more accessible')
         else:
             CWConstraintDelOp(self._cw, rdef=rdef, oldcstr=cstr)