diff --git a/bin/osv/orm.py b/bin/osv/orm.py
index 0f6253a2e09..0037c2e7de0 100644
--- a/bin/osv/orm.py
+++ b/bin/osv/orm.py
@@ -2525,7 +2525,7 @@ class orm(orm_template):
                             raise except_orm('Programming Error', ('There is no reference available for %s') % (f._obj,))
                         ref = self.pool.get(f._obj)._table
 #                        ref = f._obj.replace('.', '_')
-                        cr.execute('CREATE TABLE "%s" ("%s" INTEGER NOT NULL REFERENCES "%s" ON DELETE CASCADE, "%s" INTEGER NOT NULL REFERENCES "%s" ON DELETE CASCADE) WITH OIDS' % (f._rel, f._id1, self._table, f._id2, ref))
+                        cr.execute('CREATE TABLE "%s" ("%s" INTEGER NOT NULL REFERENCES "%s" ON DELETE CASCADE, "%s" INTEGER NOT NULL REFERENCES "%s" ON DELETE CASCADE, UNIQUE("%s","%s")) WITH OIDS' % (f._rel, f._id1, self._table, f._id2, ref, f._id1, f._id2))
                         cr.execute('CREATE INDEX "%s_%s_index" ON "%s" ("%s")' % (f._rel, f._id1, f._rel, f._id1))
                         cr.execute('CREATE INDEX "%s_%s_index" ON "%s" ("%s")' % (f._rel, f._id2, f._rel, f._id2))
                         cr.execute("COMMENT ON TABLE \"%s\" IS 'RELATION BETWEEN %s AND %s'" % (f._rel, self._table, ref))