diff --git a/mrbgems/mruby-errno/mrbgem.rake b/mrbgems/mruby-errno/mrbgem.rake
index eb39f4652..9bf6c27ab 100644
--- a/mrbgems/mruby-errno/mrbgem.rake
+++ b/mrbgems/mruby-errno/mrbgem.rake
@@ -1,4 +1,5 @@
 MRuby::Gem::Specification.new('mruby-errno') do |spec|
   spec.license = 'MIT'
   spec.authors = 'Internet Initiative Japan Inc.'
+  spec.summary = 'Errno module and SystemCallError class'
 end