Timeout_value error in process when using timer:sleep(rand:uniform()*1000)

Trying to use timer:sleep(rand:uniform()*1000) in Erlang to create a random sleep period, but receive the following error:

Error in process <0.45.0> with exit value:
{timeout_value,[{timer,sleep,1,[{file,"timer.erl"}}]

Why might I be receiving this error?