gem install fails on rubinius 3.28 / ruby 2.3.1

[tlahti]

root@a-excel:/usr/local/src/rubinius-3.28/bin# ruby --version
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-linux]
root@a-excel:/usr/local/src/rubinius-3.28/bin# ./rbx --version
rubinius 3.28 (2.2.2 20938ee8 2016-04-24 3.3) [x86_64-linux-gnu]
root@a-excel:/usr/local/src/rubinius-3.28/bin# ./gem install rbczmq
ERROR:  Error installing rbczmq:
    invalid gem: package is corrupt, exception while verifying: (<unknown>): control characters are not allowed at line 1 column 1 (Psych::SyntaxError) in /usr/local/src/rubinius-3.28/gems/cache/rbczmq-1.7.9.gem
root@a-excel:/usr/local/src/rubinius-3.28/bin#