diff --git a/mrbgems/mruby-set/mrbgem.rake b/mrbgems/mruby-set/mrbgem.rake
index 1533ebc32..1495b34ba 100644
--- a/mrbgems/mruby-set/mrbgem.rake
+++ b/mrbgems/mruby-set/mrbgem.rake
@@ -1,6 +1,7 @@
 MRuby::Gem::Specification.new('mruby-set') do |spec|
   spec.license = 'MIT'
   spec.authors = 'yui-knk'
+  spec.summary = 'Set class'
   spec.build.defines << "MRB_USE_SET"
 
   spec.add_dependency "mruby-hash-ext", :core => "mruby-hash-ext"