Clojure: Simple factorial causes stack overflow

What am I doing wrong? Simple recursion a few thousand calls deep throws a StackOverflowError.

If the limit of Clojure recursions is so low, how can I rely on it?

(defn fact[x]
  (if (<= x 1) 1 (* x  (fact (- x 1))  )))

user=> (fact 2)
2

user=> (fact 4)
24

user=> (fact 4000)
java.lang.StackOverflowError (NO_SOURCE_FILE:0)