diff --git a/mrbgem.rake b/mrbgem.rake
index 3d07f31..45ae8d2 100644
--- a/mrbgem.rake
+++ b/mrbgem.rake
@@ -10,4 +10,6 @@ MRuby::Gem::Specification.new('mjruby') do |spec|
   spec.add_dependency 'mruby-string-ext', :core => 'mruby-string-ext'
   spec.add_dependency 'mruby-io', :mgem => 'mruby-io'
   spec.add_dependency 'mruby-jvm', :github => 'jkutner/mruby-jvm'
+
+  spec.cc.include_paths << "#{spec.build.gem_clone_dir}/mruby-io/include"
 end