diff --git a/bt/includes/init_tr.php b/bt/includes/init_tr.php
index a109f5ac..17b7e6a1 100644
--- a/bt/includes/init_tr.php
+++ b/bt/includes/init_tr.php
@@ -439,6 +439,10 @@ class sql_db
 				bb_log($msg . LOG_LF, 'sql_slow_tr');
 			}
 		}
+		else
+		{
+			error_exit("[MySQL] Invalid debug mode: $mode");
+		}
 	}
 
 	/**