diff --git a/ext/bzip2/extconf.rb b/ext/bzip2/extconf.rb
index b4d93c4..fe41a07 100644
--- a/ext/bzip2/extconf.rb
+++ b/ext/bzip2/extconf.rb
@@ -3,7 +3,7 @@
 dir_config('bz2')
 have_header('bzlib.h')
 
-$CFLAGS << ' -Wall -Wextra -Wno-unused -funroll-loops '
+$CFLAGS << ' -Wall -Wextra -Wno-unused -funroll-loops -DRUBINIUS'
 # $CFLAGS << ' -O0 -ggdb -Wextra'
 
 if have_library("bz2", "BZ2_bzWriteOpen")