Error 404 while using sis_user_id to query for specific user.

[tomasz_sowinski]

I am on a second day of getting to know Canvas API.

the following URI returns 404 error

https://Canvas.instructure.com/api/v1/accounts/112233/users/sis_user_id:12345 

while 

https://Canvas.instructure.com/api/v1/accounts/112233/users

are happy to return a number of users.

What am I doing wrong?

Thanks

Tom