diff --git a/node.c b/node.c
index a5c04aa5fd..4770f7cfd2 100644
--- a/node.c
+++ b/node.c
@@ -1034,7 +1034,7 @@ rb_node_init(NODE *n, enum node_type type, VALUE a0, VALUE a1, VALUE a2)
 
 typedef struct node_buffer_elem_struct {
     struct node_buffer_elem_struct *next;
-    NODE buf[1]; /* flexible array */
+    NODE buf[FLEX_ARY_LEN];
 } node_buffer_elem_t;
 
 struct node_buffer_struct {
@@ -1046,7 +1046,7 @@ struct node_buffer_struct {
 static node_buffer_t *
 rb_node_buffer_new(void)
 {
-    node_buffer_t *nb = xmalloc(offsetof(node_buffer_t, body) + offsetof(node_buffer_elem_t, buf) + 16 * sizeof(NODE));
+    node_buffer_t *nb = xmalloc(sizeof(node_buffer_t) + 16 * sizeof(NODE));
     nb->idx = 0;
     nb->len = 16;
     nb->head = &nb->body;