sleep with too big integer compiles but doesn't work

[mlvzk]

My crystal version:

$ crystal -v
Crystal 0.27.0 (2018-11-02)

LLVM: 6.0.1
Default target: x86_64-pc-linux-gnu

Code to reproduce the bug:

puts "1"
sleep 1231231231231
puts "2"

The above code prints "2" instantly after "1".

For integers that are bigger than UInt64 the compiler returns an error, which is good:
Syntax error in test.cr:2: 1231231231231231231231 doesn't fit in an UInt64
But my code compiles and doesn't work as expected.

I also checked if it works on play.crystal-lang.org, and it doesn't: https://play.crystal-lang.org/#/r/5v3m