diff --git a/CRM/Admin/Form/Extensions.php b/CRM/Admin/Form/Extensions.php
index 4b93cc02a0d..09e78f8ff2f 100644
--- a/CRM/Admin/Form/Extensions.php
+++ b/CRM/Admin/Form/Extensions.php
@@ -45,7 +45,7 @@ public function preProcess() {
     $this->_key = CRM_Utils_Request::retrieve('key', 'String',
       $this, FALSE, 0
     );
-    if (!preg_match('/[0-9a-zA-Z._-]+/', $this->_key)) {
+    if (!preg_match('/^[0-9a-zA-Z._-]+$/', $this->_key)) {
       throw new CRM_Core_Exception('Extension Key does not match expected standard');
     }
     $session = CRM_Core_Session::singleton();