diff --git a/packages/playwright-core/src/server/bidi/bidiBrowser.ts b/packages/playwright-core/src/server/bidi/bidiBrowser.ts
index 238b0e2858..7af8150c9d 100644
--- a/packages/playwright-core/src/server/bidi/bidiBrowser.ts
+++ b/packages/playwright-core/src/server/bidi/bidiBrowser.ts
@@ -20,7 +20,7 @@ import { BrowserContext, assertBrowserContextIsNotOwned, verifyGeolocation } fro
 import * as network from '../network';
 import { BidiConnection } from './bidiConnection';
 import { bidiBytesValueToString } from './bidiNetworkManager';
-import { addMainBinding, BidiPage, kPlaywrightBindingChannel } from './bidiPage';
+import { addMainBindingSource, BidiPage, kPlaywrightBindingChannel } from './bidiPage';
 import * as bidi from './third_party/bidiProtocol';
 
 import type { RegisteredListener } from '../utils/eventsHelper';
@@ -238,7 +238,6 @@ export class BidiBrowserContext extends BrowserContext {
 
   // TODO: consider calling this only when bindings are added.
   private async _installMainBinding() {
-    const functionDeclaration = addMainBinding.toString();
     const args: bidi.Script.ChannelValue[] = [{
       type: 'channel',
       value: {
@@ -247,7 +246,7 @@ export class BidiBrowserContext extends BrowserContext {
       }
     }];
     await this._browser._browserSession.send('script.addPreloadScript', {
-      functionDeclaration,
+      functionDeclaration: addMainBindingSource,
       arguments: args,
       userContexts: [this._userContextId()],
     });
diff --git a/packages/playwright-core/src/server/bidi/bidiPage.ts b/packages/playwright-core/src/server/bidi/bidiPage.ts
index 50e45d1352..a9affaebec 100644
--- a/packages/playwright-core/src/server/bidi/bidiPage.ts
+++ b/packages/playwright-core/src/server/bidi/bidiPage.ts
@@ -328,7 +328,7 @@ export class BidiPage implements PageDelegate {
     // For non-persistent context, the main binding is installed during context creation.
     if (this._browserContext._browserContextId)
       return;
-    const functionDeclaration = addMainBinding.toString();
+    const functionDeclaration = addMainBindingSource;
     const args: bidi.Script.ChannelValue[] = [{
       type: 'channel',
       value: {
@@ -572,9 +572,8 @@ export class BidiPage implements PageDelegate {
   }
 }
 
-export function addMainBinding(callback: (arg: any) => void) {
-  (globalThis as any)[PageBinding.kPlaywrightBinding] = callback;
-}
+export const addMainBindingSource =
+  `function addMainBinding(callback) { globalThis['${PageBinding.kPlaywrightBinding}'] = callback; }`;
 
 function toBidiExecutionContext(executionContext: dom.FrameExecutionContext): BidiExecutionContext {
   return executionContext.delegate as BidiExecutionContext;