diff --git a/mrbgems/mruby-symbol-ext/mrblib/symbol.rb b/mrbgems/mruby-symbol-ext/mrblib/symbol.rb
index 78edf3cad..51a8ddc84 100644
--- a/mrbgems/mruby-symbol-ext/mrblib/symbol.rb
+++ b/mrbgems/mruby-symbol-ext/mrblib/symbol.rb
@@ -1,4 +1,5 @@
 class Symbol
+  include Comparable
 
   def to_proc
     ->(obj,*args,&block) do