diff --git a/.travis.yml b/.travis.yml
index 8cab4ec..f675921 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -50,6 +50,7 @@ before_script:
       composer global require wp-coding-standards/wpcs
       phpcs --config-set installed_paths $HOME/.composer/vendor/wp-coding-standards/wpcs
     fi
+  - composer install --prefer-source
 
 script:
   - |