diff --git a/lib/stages/prepare_build.sh b/lib/stages/prepare_build.sh
index d2c5f0b..7237d50 100644
--- a/lib/stages/prepare_build.sh
+++ b/lib/stages/prepare_build.sh
@@ -73,4 +73,5 @@ _stage_prepare_build() {
     composer config allow-plugins.composer/installers true --no-plugins --working-dir="${DRUPAL_TESTING_DRUPAL_INSTALLATION_DIRECTORY}"
     composer config allow-plugins.oomphinc/composer-installers-extender true --no-plugins --working-dir="${DRUPAL_TESTING_DRUPAL_INSTALLATION_DIRECTORY}"
     composer config allow-plugins.dealerdirect/phpcodesniffer-composer-installer true --no-plugins --working-dir="${DRUPAL_TESTING_DRUPAL_INSTALLATION_DIRECTORY}"
+    composer config allow-plugins.phpstan/extension-installer true --no-plugins --working-dir="${DRUPAL_TESTING_DRUPAL_INSTALLATION_DIRECTORY}"
 }