OpenSSL::Digest::SHA256 fails with thin when thin loaded before openssl

When thin is loaded before openssl then OpenSSL::Digest::SHA256 won't work.

How to reproduce

require 'rubygems'
require 'thin'
require 'openssl'
p OpenSSL::Digest::SHA256.digest("hello wolrd") # will fail

Workaround

Load openssl before thin (e.g. bin/thin)

require 'rubygems'
require 'openssl'
require 'thin'
p OpenSSL::Digest::SHA256.digest("hello wolrd") # SUCCESS!

Any thoughts?
I could provide some straces if needed

Kind regards
Peter