diff --git a/src/line/rich-menu.ts b/src/line/rich-menu.ts
index c693778ddfc..6fa391de5ba 100644
--- a/src/line/rich-menu.ts
+++ b/src/line/rich-menu.ts
@@ -10,6 +10,7 @@ type RichMenuRequest = messagingApi.RichMenuRequest;
 type RichMenuResponse = messagingApi.RichMenuResponse;
 type RichMenuArea = messagingApi.RichMenuArea;
 type Action = messagingApi.Action;
+const USER_BATCH_SIZE = 500;
 
 export interface RichMenuSize {
   width: 2500;
@@ -66,6 +67,14 @@ function getBlobClient(opts: RichMenuOpts = {}): messagingApi.MessagingApiBlobCl
   });
 }
 
+function chunkUserIds(userIds: string[]): string[][] {
+  const batches: string[][] = [];
+  for (let i = 0; i < userIds.length; i += USER_BATCH_SIZE) {
+    batches.push(userIds.slice(i, i + USER_BATCH_SIZE));
+  }
+  return batches;
+}
+
 /**
  * Create a new rich menu
  * @returns The rich menu ID
@@ -187,13 +196,7 @@ export async function linkRichMenuToUsers(
 ): Promise<void> {
   const client = getClient(opts);
 
-  // LINE allows max 500 users per request
-  const batches = [];
-  for (let i = 0; i < userIds.length; i += 500) {
-    batches.push(userIds.slice(i, i + 500));
-  }
-
-  for (const batch of batches) {
+  for (const batch of chunkUserIds(userIds)) {
     await client.linkRichMenuIdToUsers({
       richMenuId,
       userIds: batch,
@@ -230,13 +233,7 @@ export async function unlinkRichMenuFromUsers(
 ): Promise<void> {
   const client = getClient(opts);
 
-  // LINE allows max 500 users per request
-  const batches = [];
-  for (let i = 0; i < userIds.length; i += 500) {
-    batches.push(userIds.slice(i, i + 500));
-  }
-
-  for (const batch of batches) {
+  for (const batch of chunkUserIds(userIds)) {
     await client.unlinkRichMenuIdFromUsers({
       userIds: batch,
     });