SQL Server - Assign default DateTime value to parameters in Stored Procedure

Maybe I'm being an idiot here, but I'm trying to assign a default DateTime value to a Stored Procedure in MS SQL Server 2005 but can't get it to work eg:

CREATE PROCEDURE MyProcedure
(
    @MyInteger    INT = 123,
    @MyDateTime   DATETIME = CONVERT(DATETIME, '1753-01-01 00:00:00', 20)
)
AS
BEGIN ... (snip)

So if the @MyDateTime input parameter isn't specified, it should use '1753-01-01 00:00:00' by default, but I get the err开发者_Python百科or...

Incorrect syntax near the keyword 'CONVERT'.

I can get it to work for Integers just fine. What am I doing wrong?

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Edit: from the answers below, I eventually went with the following inside the Sproc itself:

CREATE PROCEDURE MyProcedure
(
    @MyInteger    INT = 123,
    @MyDateTime   DATETIME = NULL
)
AS
BEGIN
    SET NOCOUNT ON

    SET @MyDateTime = COALESCE(@MyDateTime, CONVERT(DATETIME, '1753-01-01 00:00:00', 20))

    ...snip...
END

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@MyDateTime DATETIME ='1753-01-01 00:00:00'

Or right within the sproc you can do this:

SELECT @MyDateTime = (SELECT CONVERT(DATETIME, '1753-01-01 00:00:00', 20))

The error is due to calling CONVERT, which you cannot do when defaulting parameters.

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You can't have the CONVERT() function call in there, just assign the default value using the relevent datetime string.