Count Distinct Over Partition Syntax Error

Count(Distinct [field]) over (partition by [field2]) returns a syntax error at the key word distinct

Count(all [field]) over (partition by [field2]) compiles fine

I am writing a query to count the number of clients a sales rep has when the sales rep represents multiple companies (ad agency).  I need a count of the clients each company has and a distinct count that each rep has.  A client may be assigned to multiple companies.

Is a distinct count supported with partitions?