Hi there, The problem was effectively due to my misreading of libffi's documentation for return values (which are handled differently from parameters). Thanks for your help identifying the problem. You should probably close the bug. Thanks, Etienne (upstream SableVM author) -- Etienne M. Gagnon, Ph.D. http://www.info.uqam.ca/~egagnon/ SableVM: http://www.sablevm.org/ SableCC: http://www.sablecc.org/