diff --git a/PHPCI/Plugin/Shell.php b/PHPCI/Plugin/Shell.php
index 602824ec..83595ad8 100644
--- a/PHPCI/Plugin/Shell.php
+++ b/PHPCI/Plugin/Shell.php
@@ -41,6 +41,10 @@ class Shell implements \PHPCI\Plugin
     */
     public function execute()
     {
+        if (!defined('ENABLE_SHELL_PLUGIN') || !ENABLE_SHELL_PLUGIN) {
+            throw new \Exception('The shell plugin is not enabled.');
+        }
+        
         $success = $this->phpci->executeCommand($this->command);
         
         return $success;