diff --git a/src/DrupalCI/Plugin/BuildSteps/generic/Composer.php b/src/DrupalCI/Plugin/BuildSteps/generic/Composer.php
index b962dd4..e6a3df7 100644
--- a/src/DrupalCI/Plugin/BuildSteps/generic/Composer.php
+++ b/src/DrupalCI/Plugin/BuildSteps/generic/Composer.php
@@ -23,7 +23,7 @@ class Composer extends ContainerCommand {
   }
 
   protected function buildComposerCommand($input, $data) {
-    return "composer.phar --working-dir core --prefer-dist $data";
+    return "composer.phar $data";
   }
 
 }
diff --git a/src/DrupalCI/Plugin/Preprocess/definition/DrupalInstall.php b/src/DrupalCI/Plugin/Preprocess/definition/DrupalInstall.php
index ee73365..b406bf1 100644
--- a/src/DrupalCI/Plugin/Preprocess/definition/DrupalInstall.php
+++ b/src/DrupalCI/Plugin/Preprocess/definition/DrupalInstall.php
@@ -15,12 +15,11 @@ class DrupalInstall {
    * {@inheritdoc}
    */
   public function process(array &$definition, $value) {
-    $composer_commands = array('install', 'update');
-    if (in_array($value, $composer_commands)) {
-      $definition['install']['composer'] = $value;
+    if (!empty($value)) {
+      $definition['install']['composer'][] = $value;
     }
     else {
-      $definition['install']['composer'] = 'install';
+      $definition['install']['composer'][] = '--working-dir core --prefer-dist install';
     }
   }