diff --git a/addons/xterm-addon-serialize/src/SerializeAddon.ts b/addons/xterm-addon-serialize/src/SerializeAddon.ts
index 60fe9624..25fa9ad2 100644
--- a/addons/xterm-addon-serialize/src/SerializeAddon.ts
+++ b/addons/xterm-addon-serialize/src/SerializeAddon.ts
@@ -412,25 +412,5 @@ export class SerializeAddon implements ITerminalAddon {
       + alternativeScreenContent;
   }
 
-  // this is a util used only for test
-  private static _inspectBuffer(buffer: IBuffer): { x: number, y: number, data: any[][] } {
-    const lines: any[] = [];
-
-    for (let i = 0; i < buffer.length; i++) {
-      /**
-       * Do this intentionally to get content of underlining source
-       */
-      const bufferLine = (buffer.getLine(i)! as any)._line;
-
-      lines.push(JSON.stringify(bufferLine));
-    }
-
-    return {
-      x: buffer.cursorX,
-      y: buffer.cursorY,
-      data: lines
-    };
-  }
-
   public dispose(): void { }
 }
diff --git a/addons/xterm-addon-serialize/test/SerializeAddon.api.ts b/addons/xterm-addon-serialize/test/SerializeAddon.api.ts
index 5dc29d0d..339ac162 100644
--- a/addons/xterm-addon-serialize/test/SerializeAddon.api.ts
+++ b/addons/xterm-addon-serialize/test/SerializeAddon.api.ts
@@ -18,12 +18,12 @@ const writeRawSync = (page: any, str: string): Promise<void> => writeSync(page,
 
 const testNormalScreenEqual = async (page: any, str: string): Promise<void> => {
   await writeRawSync(page, str);
-  const originalBuffer = await page.evaluate(`SerializeAddon._inspectBuffer(term.buffer.normal);`);
+  const originalBuffer = await page.evaluate(`SerializeAddonTestUtil.inspectBuffer(term.buffer.normal);`);
 
   const result = await page.evaluate(`serializeAddon.serialize();`) as string;
   await page.evaluate(`term.reset();`);
   await writeRawSync(page, result);
-  const newBuffer = await page.evaluate(`SerializeAddon._inspectBuffer(term.buffer.normal);`);
+  const newBuffer = await page.evaluate(`SerializeAddonTestUtil.inspectBuffer(term.buffer.normal);`);
 
   // chai decides -0 and 0 are different number...
   // and firefox have a bug that output -0 for unknown reason
@@ -51,11 +51,11 @@ describe('SerializeAddon', () => {
 
   it('produce different output when we call test util with different text', async function(): Promise<any> {
     await writeRawSync(page, '12345');
-    const buffer1 = await page.evaluate(`SerializeAddon._inspectBuffer(term.buffer.normal);`);
+    const buffer1 = await page.evaluate(`SerializeAddonTestUtil.inspectBuffer(term.buffer.normal);`);
 
     await page.evaluate(`term.reset();`);
     await writeRawSync(page, '67890');
-    const buffer2 = await page.evaluate(`SerializeAddon._inspectBuffer(term.buffer.normal);`);
+    const buffer2 = await page.evaluate(`SerializeAddonTestUtil.inspectBuffer(term.buffer.normal);`);
 
     assert.throw(() => {
       assert.equal(JSON.stringify(buffer1), JSON.stringify(buffer2));
@@ -64,11 +64,11 @@ describe('SerializeAddon', () => {
 
   it('produce different output when we call test util with different line wrap', async function(): Promise<any> {
     await writeRawSync(page, '1234567890\r\n12345');
-    const buffer3 = await page.evaluate(`SerializeAddon._inspectBuffer(term.buffer.normal);`);
+    const buffer3 = await page.evaluate(`SerializeAddonTestUtil.inspectBuffer(term.buffer.normal);`);
 
     await page.evaluate(`term.reset();`);
     await writeRawSync(page, '1234567890n12345');
-    const buffer4 = await page.evaluate(`SerializeAddon._inspectBuffer(term.buffer.normal);`);
+    const buffer4 = await page.evaluate(`SerializeAddonTestUtil.inspectBuffer(term.buffer.normal);`);
 
     assert.throw(() => {
       assert.equal(JSON.stringify(buffer3), JSON.stringify(buffer4));
diff --git a/addons/xterm-addon-serialize/test/SerializeAddonTestUtil.ts b/addons/xterm-addon-serialize/test/SerializeAddonTestUtil.ts
new file mode 100644
index 00000000..23ac2237
--- /dev/null
+++ b/addons/xterm-addon-serialize/test/SerializeAddonTestUtil.ts
@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2021 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { IBuffer } from 'xterm';
+export class SerializeAddonTestUtil {
+  // this is a util used only for test
+  public static inspectBuffer(buffer: IBuffer): { x: number, y: number, data: any[][] } {
+    const lines: any[] = [];
+
+    for (let i = 0; i < buffer.length; i++) {
+      /**
+       * Do this intentionally to get content of underlining source
+       */
+      const bufferLine = (buffer.getLine(i)! as any)._line;
+
+      lines.push(JSON.stringify(bufferLine));
+    }
+
+    return {
+      x: buffer.cursorX,
+      y: buffer.cursorY,
+      data: lines
+    };
+  }
+}
diff --git a/demo/client.ts b/demo/client.ts
index 93b7c26c..27d1c297 100644
--- a/demo/client.ts
+++ b/demo/client.ts
@@ -13,6 +13,7 @@ import { AttachAddon } from '../addons/xterm-addon-attach/out/AttachAddon';
 import { FitAddon } from '../addons/xterm-addon-fit/out/FitAddon';
 import { SearchAddon, ISearchOptions } from '../addons/xterm-addon-search/out/SearchAddon';
 import { SerializeAddon } from '../addons/xterm-addon-serialize/out/SerializeAddon';
+import { SerializeAddonTestUtil } from '../addons/xterm-addon-serialize/out-test/SerializeAddonTestUtil';
 import { WebLinksAddon } from '../addons/xterm-addon-web-links/out/WebLinksAddon';
 import { WebglAddon } from '../addons/xterm-addon-webgl/out/WebglAddon';
 import { Unicode11Addon } from '../addons/xterm-addon-unicode11/out/Unicode11Addon';
@@ -38,6 +39,7 @@ export interface IWindowWithTerminal extends Window {
   FitAddon?: typeof FitAddon;
   SearchAddon?: typeof SearchAddon;
   SerializeAddon?: typeof SerializeAddon;
+  SerializeAddonTestUtil?: typeof SerializeAddonTestUtil;
   WebLinksAddon?: typeof WebLinksAddon;
   WebglAddon?: typeof WebglAddon;
   Unicode11Addon?: typeof Unicode11Addon;
@@ -132,6 +134,7 @@ if (document.location.pathname === '/test') {
   window.FitAddon = FitAddon;
   window.SearchAddon = SearchAddon;
   window.SerializeAddon = SerializeAddon;
+  window.SerializeAddonTestUtil = SerializeAddonTestUtil;
   window.Unicode11Addon = Unicode11Addon;
   window.WebLinksAddon = WebLinksAddon;
   window.WebglAddon = WebglAddon;