diff --git a/.travis.yml b/.travis.yml
index 08ae96d18..f18d77f0b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -13,7 +13,7 @@ before_install:
   - rvm install 2.6.0
   - rvm use 2.6.0
 install:
-  - gem install pdd
+  - gem install pdd -v 0.20.5
   - gem install xcop
   - gem install est
 env: