Hive unable to manually set number of reducers

I have the following hive query:

select count(distinct id) as total from mytable;

which automatically spawns:
1408 Mappers
1 Reducer

I need to manually set the number of reducers and I have tried the following:

set mapred.reduce.tasks=50 
set hive.exec.reducers.max=50

but none of these settings seem to be honored. The query takes forever to run. Is there a way to manually set the reducers or maybe rewrite the query so it can result in more reducers? Thanks!