diff --git a/.travis.yml b/.travis.yml
index 2eb5d76..65e5df8 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -22,7 +22,7 @@ before_script:
 
 script:
   - vendor/bin/phpcs --standard=psr2 src/
-  - vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover
+  - XDEBUG_MODE=coverage vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover
 
 after_script:
   - wget https://scrutinizer-ci.com/ocular.phar