Problem Renaming Default Constraints In Schema Other Than Dbo

Does anyone know how to tell sp_rename to look in a schema other than the default.
The code below reproduces the problem.

-- WORKS IN default schema
--
create table dbo.TestDF1(
dfField intconstraint DF1 default 0
)
go

sp_rename 'DF1', 'DF2', 'OBJECT'
go

Select name
From
sys.default_constraints
where
object_name(parent_object_id) = 'TestDF1'
go

drop table dbo.TestDF1
go

-- DOESN'T WORK IN added schema
--
create schema TestSchema
go

create table TestSchema.TestDF2(
dfField intconstraint DF3 default 0
)
go

sp_rename 'DF3', 'DF4', 'OBJECT'
go

Msg 15248, Level 11, State 1, Procedure sp_rename, Line 315
Either the parameter @objname is ambiguous or the claimed @objtype (OBJECT) is wrong.
---------------------------
drop table TestSchema.TestDF2
go

drop schema TestSchema
go