diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 09b219cdde73ecda83fb94b841a45138ecb2ad77..e055c66d73756b2bd492026adbdca2a6a5569f8c 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -11,20 +11,32 @@ before_script:
   - apt-get -yqq update
 
   # install the required packages for the running CI tests
-  - apt-get -yqqf install zip unzip subversion mysql-client --fix-missing
+  - |
+    apt-get -yqqf install zip unzip subversion mysql-client --fix-missing
+
+    if [[ $(lsb_relase -a) =~ "stretch" ]]; then
+      apt-get -yqqf install default-libmysqlclient-dev --fix-missing
+    else
+      apt-get -yqqf install libmysqlclient-dev --fix-missing
+    fi
 
   # PHP extensions
-  - docker-php-ext-install mbstring
-  - docker-php-ext-enable mbstring mysqli pdo_mysql intl gd zip bz2
+  - docker-php-ext-install mbstring mysqli
+  - docker-php-ext-enable mbstring mysqli intl gd zip bz2
 
   # Install Composer
   - curl -sS https://getcomposer.org/installer | php
 
   # Set up WordPress tests
-  - bash bin/install-wp-tests.sh wordpress_tests root mysql mysql latest true
+  - bash bin/install-wp-tests.sh $MYSQL_DATABASE root $MYSQL_ROOT_PASSWORD mysql latest true
 
-  # PHPUnit for most builds
-  - php composer.phar global require "phpunit/phpunit=6.1.*"
+  # PHPUnit
+  - |
+    if [[ $(php -v) =~ "^PHP 7" ]]; then
+      php composer.phar global require "phpunit/phpunit=6.1.*"
+    else
+      php composer.phar global require "phpunit/phpunit=4.8.*"
+    fi
 
   # Install PHPCS and WPCS
   - php composer.phar global require automattic/vipwpcs
@@ -35,7 +47,6 @@ PHPunit:PHP5.3:MySQL:
   services:
     - mysql:5.6
   script:
-    - php composer.phar global require "phpunit/phpunit=4.8.*"
     - phpcs
     - phpunit
   allow_failure: true
@@ -45,7 +56,6 @@ PHPunit:PHP5.6:MySQL:
   services:
     - mysql:5.6
   script:
-    - php composer.phar global require "phpunit/phpunit=4.8.*"
     - phpcs
     - phpunit