A build error occurs when I specified i386 arch only. x86_64 arch only or Universal Binary build succeeded. $ RC_ARCHS=i386 rake jobs=2 --- snip --- ./miniruby -I. -I./lib bin/rubyc --internal --arch i386 -C "ext/ripper/lib/ripper/sexp.rb" -o "ext/ripper/lib/ripper/sexp.rbo" ./miniruby -I. -I./lib bin/rubyc --internal --arch i386 -C "ext/ripper/lib/ripper.rb" -o "ext/ripper/lib/ripper.rbo" cd ext/bigdecimal && ../../miniruby -I../.. -I../../lib -r rbconfig -e "RbConfig::CONFIG['libdir'] = '../..'; require './extconf.rb'"cd ext/digest/bubblebabble && ../../../miniruby -I../../.. -I../../../lib -r rbconfig -e "RbConfig::CONFIG['libdir'] = '../../..'; require './extconf.rb'" Assertion failed: (((NumArgs == FTy->getNumParams()) || (FTy->isVarArg() && NumArgs > FTy->getNumParams())) && "Invoking a function with bad signature"), function init, file Instructions.cpp, line 559. Assertion failed: (((NumArgs == FTy->getNumParams()) || (FTy->isVarArg() && NumArgs > FTy->getNumParams())) && "Invoking a function with bad signature"), function init, file Instructions.cpp, line 559. sh: line 1: 23500 Abort trap ../../miniruby -I../.. -I../../lib -r rbconfig -e "RbConfig::CONFIG['libdir'] = '../..'; require './extconf.rb'" sh: line 1: 23501 Abort trap ../../../miniruby -I../../.. -I../../../lib -r rbconfig -e "RbConfig::CONFIG['libdir'] = '../../..'; require './extconf.rb'" rake aborted! Command failed with status (134): [cd ext/bigdecimal && ../../miniruby -I../....] (See full trace by running task with --trace)