diff --git a/packages/@n8n/task-runner/src/js-task-runner/__tests__/result-validation.test.ts b/packages/@n8n/task-runner/src/js-task-runner/__tests__/result-validation.test.ts
index 7112468863..324ff6f749 100644
--- a/packages/@n8n/task-runner/src/js-task-runner/__tests__/result-validation.test.ts
+++ b/packages/@n8n/task-runner/src/js-task-runner/__tests__/result-validation.test.ts
@@ -28,6 +28,7 @@ describe('result validation', () => {
 			['binary', {}],
 			['pairedItem', {}],
 			['error', {}],
+			['index', {}], // temporarily allowed until refactored out
 		])(
 			'should not throw an error if the output item has %s key in addition to json',
 			(key, value) => {
diff --git a/packages/@n8n/task-runner/src/js-task-runner/result-validation.ts b/packages/@n8n/task-runner/src/js-task-runner/result-validation.ts
index 4453521bf7..17c4df9a6e 100644
--- a/packages/@n8n/task-runner/src/js-task-runner/result-validation.ts
+++ b/packages/@n8n/task-runner/src/js-task-runner/result-validation.ts
@@ -4,7 +4,19 @@ import type { INodeExecutionData } from 'n8n-workflow';
 import { ValidationError } from './errors/validation-error';
 import { isObject } from './obj-utils';
 
-export const REQUIRED_N8N_ITEM_KEYS = new Set(['json', 'binary', 'pairedItem', 'error']);
+export const REQUIRED_N8N_ITEM_KEYS = new Set([
+	'json',
+	'binary',
+	'pairedItem',
+	'error',
+
+	/**
+	 * The `index` key was added accidentally to Function, FunctionItem, Gong,
+	 * Execute Workflow, and ToolWorkflowV2, so we need to allow it temporarily.
+	 * Once we stop using it in all nodes, we can stop allowing the `index` key.
+	 */
+	'index',
+]);
 
 function validateTopLevelKeys(item: INodeExecutionData, itemIndex: number) {
 	for (const key in item) {
diff --git a/packages/nodes-base/nodes/Code/Sandbox.ts b/packages/nodes-base/nodes/Code/Sandbox.ts
index e11a078f54..b3e3057d23 100644
--- a/packages/nodes-base/nodes/Code/Sandbox.ts
+++ b/packages/nodes-base/nodes/Code/Sandbox.ts
@@ -22,7 +22,19 @@ export interface SandboxContext extends IWorkflowDataProxyData {
 	helpers: IExecuteFunctions['helpers'];
 }
 
-export const REQUIRED_N8N_ITEM_KEYS = new Set(['json', 'binary', 'pairedItem', 'error']);
+export const REQUIRED_N8N_ITEM_KEYS = new Set([
+	'json',
+	'binary',
+	'pairedItem',
+	'error',
+
+	/**
+	 * The `index` key was added accidentally to Function, FunctionItem, Gong,
+	 * Execute Workflow, and ToolWorkflowV2, so we need to allow it temporarily.
+	 * Once we stop using it in all nodes, we can stop allowing the `index` key.
+	 */
+	'index',
+]);
 
 export function getSandboxContext(
 	this: IExecuteFunctions | ISupplyDataFunctions,
diff --git a/packages/nodes-base/nodes/Code/test/Code.node.test.ts b/packages/nodes-base/nodes/Code/test/Code.node.test.ts
index 486b6b673d..595e4d177e 100644
--- a/packages/nodes-base/nodes/Code/test/Code.node.test.ts
+++ b/packages/nodes-base/nodes/Code/test/Code.node.test.ts
@@ -40,6 +40,13 @@ describe('Code Node unit test', () => {
 					[{ json: { count: 42 } }],
 					[{ json: { count: 42 } }],
 				],
+
+				// temporarily allowed until refactored out
+				'should handle an index key': [
+					[{ json: { count: 42 }, index: 0 }],
+					[{ json: { count: 42 }, index: 0 }],
+				],
+
 				'should handle when returned data is not an array': [
 					{ json: { count: 42 } },
 					[{ json: { count: 42 } }],