diff --git a/ext/mysqlnd/mysqlnd_palloc.h b/ext/mysqlnd/mysqlnd_palloc.h
index 5a1228366d2..f84fcc38efb 100644
--- a/ext/mysqlnd/mysqlnd_palloc.h
+++ b/ext/mysqlnd/mysqlnd_palloc.h
@@ -68,6 +68,8 @@ typedef struct st_mysqlnd_zval {
 
 typedef struct st_mysqlnd_ndzval_list {
 	mysqlnd_zval 	**ptr_line;		/* we allocate this, all are pointers to the block */
+	void			*canary1;
+	void			*canary2;
 	mysqlnd_zval	**last_added;	/* this points to the ptr_line, and moves left-right. It's our stack */
 } mysqlnd_ndzval_list;