diff --git a/appveyor.yml b/appveyor.yml
index e963ea035..e6bef7790 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -40,5 +40,6 @@ init:
 
 build_script:
   - set MRUBY_CONFIG=appveyor_config.rb
+  - rake gensym
   - rake -m -j4
   - rake -E STDOUT.sync=true test