diff --git a/phpBB/includes/acm/acm_memory.php b/phpBB/includes/acm/acm_memory.php
index 1a672ad7e1..efbfd4dd62 100644
--- a/phpBB/includes/acm/acm_memory.php
+++ b/phpBB/includes/acm/acm_memory.php
@@ -50,6 +50,8 @@ class acm_memory
 
 		if (isset($this->function) && !function_exists($this->function))
 		{
+			global $acm_type;
+
 			trigger_error("The required function [{$this->function}] is not available for the ACM module $acm_type.", E_USER_ERROR);
 		}
 	}