diff --git a/.travis.yml b/.travis.yml
index 24e1060..5b82142 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,7 @@ matrix:
 
 install:
   - travis_retry composer install --no-interaction --prefer-dist --optimize-autoloader
-  - travis_retry composer global require phpunit/phpunit # cannot use phpunit.phar or require-dev, because this package is a phpunit dep
+  - travis_retry composer global require phpunit/phpunit ^6 # cannot use phpunit.phar or require-dev, because this package is a phpunit dep
   - travis_retry wget --no-verbose https://phar.io/releases/phive.phar
 
 script:
diff --git a/appveyor.yml b/appveyor.yml
index 25ef5c8..4ceb6ce 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -48,7 +48,7 @@ install:
   - IF NOT EXIST php-installed.txt type nul >> php-installed.txt
   - cd c:\reflectiondocblock
   - composer install --no-interaction --prefer-dist --no-progress
-  - composer global require phpunit/phpunit
+  - composer global require phpunit/phpunit ^6
   - composer global config bin-dir --absolute
 
 test_script: