diff --git a/packages/api/src/export.ts b/packages/api/src/export.ts
index e9c0879c..bbdf6b12 100644
--- a/packages/api/src/export.ts
+++ b/packages/api/src/export.ts
@@ -3,13 +3,13 @@ import {
 	isS3Failure,
 	logger,
 	TranscriptionConfig,
-	TranscriptionDynamoItem,
 } from '@guardian/transcription-service-backend-common';
 import {
 	ExportItems,
 	ExportStatus,
 	ExportStatuses,
 	ExportType,
+	TranscriptionDynamoItem,
 } from '@guardian/transcription-service-common';
 import { uploadToGoogleDocs } from './services/googleDrive';
 import { S3Client } from '@aws-sdk/client-s3';
diff --git a/packages/backend-common/src/sqs.ts b/packages/backend-common/src/sqs.ts
index 15277279..f1b52f9e 100644
--- a/packages/backend-common/src/sqs.ts
+++ b/packages/backend-common/src/sqs.ts
@@ -10,9 +10,9 @@ import {
 	OutputBucketUrls,
 	DestinationService,
 	TranscriptionJob,
-	LanguageCode,
 	TranscriptionOutput,
 	TranscriptionEngine,
+	InputLanguageCode,
 } from '@guardian/transcription-service-common';
 import {
 	getSignedUploadUrl,
@@ -67,7 +67,7 @@ export const generateOutputSignedUrlAndSendMessage = async (
 	userEmail: string,
 	originalFilename: string,
 	inputSignedUrl: string,
-	languageCode: LanguageCode,
+	languageCode: InputLanguageCode,
 	translationRequested: boolean,
 	diarizationRequested: boolean,
 ): Promise<SendResult> => {
diff --git a/packages/common/src/languages.ts b/packages/common/src/languages.ts
index a3991005..35b5d409 100644
--- a/packages/common/src/languages.ts
+++ b/packages/common/src/languages.ts
@@ -1,10 +1,9 @@
-import { z } from 'zod';
+import { getKeys } from './types';
 // languages supported by whisper.cpp
 // copied from
 // https://github.com/ggerganov/whisper.cpp/blob/25d313b38b1f562200f915cd5952555613cd0110/whisper.cpp#L251
 // and values transformed to title case
-export const languageCodeToLanguage = Object.freeze({
-	auto: 'Auto-detect language (not yet recommended)',
+const languageCodeToLanguage = {
 	en: 'English',
 	zh: 'Chinese',
 	de: 'German',
@@ -105,16 +104,18 @@ export const languageCodeToLanguage = Object.freeze({
 	jw: 'Javanese',
 	su: 'Sundanese',
 	yue: 'Cantonese',
-});
+};
 
-type LanguageCodeToLanguage = typeof languageCodeToLanguage;
+export const languageCodeToLanguageWithAuto = Object.freeze({
+	auto: 'Auto-detect language (not yet recommended)',
+	...languageCodeToLanguage,
+});
 
-// There doesn't seem to be a way to get the object keys that has a type which
-// is an array of a union of string literals rather than an array of strings.
-// https://www.charpeni.com/blog/properly-type-object-keys-and-object-entries
-export const languageCodes = Object.keys(languageCodeToLanguage) as [
-	keyof LanguageCodeToLanguage,
-];
+export const languageCodeToLanguageWithUnknown = Object.freeze({
+	UNKNOWN: 'Detected language not recognised',
+	...languageCodeToLanguage,
+});
 
-export const LanguageCode = z.enum(languageCodes);
-export type LanguageCode = z.infer<typeof LanguageCode>;
+export const languageCodes = getKeys(languageCodeToLanguage);
+export const inputLanguageCodes = getKeys(languageCodeToLanguageWithAuto);
+export const outputLanguageCodes = getKeys(languageCodeToLanguageWithUnknown);
diff --git a/packages/common/src/types.ts b/packages/common/src/types.ts
index c34799b7..6301a751 100644
--- a/packages/common/src/types.ts
+++ b/packages/common/src/types.ts
@@ -1,5 +1,5 @@
 import { z } from 'zod';
-import { LanguageCode, languageCodeToLanguage } from './languages';
+import { inputLanguageCodes, outputLanguageCodes } from './languages';
 
 // thanks https://github.com/colinhacks/zod/discussions/2125#discussioncomment-7452235
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -7,7 +7,15 @@ export function getKeys<T extends Record<string, any>>(obj: T) {
 	return Object.keys(obj) as [keyof typeof obj];
 }
 
-const zodLanguageCode = z.enum(getKeys(languageCodeToLanguage));
+export const InputLanguageCode = z.enum(inputLanguageCodes);
+export type InputLanguageCode = z.infer<typeof InputLanguageCode>;
+
+export const OutputLanguageCode = z.enum(outputLanguageCodes);
+export type OutputLanguageCode = z.infer<typeof OutputLanguageCode>;
+
+export const inputToOutputLanguageCode = (
+	c: InputLanguageCode,
+): OutputLanguageCode => (c === 'auto' ? 'UNKNOWN' : c);
 
 export enum DestinationService {
 	TranscriptionService = 'TranscriptionService',
@@ -41,7 +49,7 @@ export const MediaDownloadJob = z.object({
 	id: z.string(),
 	url: z.string(),
 	userEmail: z.string(),
-	languageCode: zodLanguageCode,
+	languageCode: InputLanguageCode,
 	translationRequested: z.boolean(),
 	diarizationRequested: z.boolean(),
 });
@@ -61,7 +69,7 @@ export const TranscriptionJob = z.object({
 	userEmail: z.string(),
 	transcriptDestinationService: z.nativeEnum(DestinationService),
 	outputBucketUrls: OutputBucketUrls,
-	languageCode: zodLanguageCode,
+	languageCode: InputLanguageCode,
 	translate: z.boolean(),
 	diarize: z.boolean(),
 	engine: z.nativeEnum(TranscriptionEngine),
@@ -80,7 +88,7 @@ const TranscriptionOutputBase = z.object({
 
 export const TranscriptionOutputSuccess = TranscriptionOutputBase.extend({
 	status: z.literal('SUCCESS'),
-	languageCode: z.string(),
+	languageCode: OutputLanguageCode,
 	outputBucketKeys: OutputBucketKeys,
 	// we can get rid of this when we switch to using a zip
 	translationOutputBucketKeys: z.optional(OutputBucketKeys),
@@ -215,7 +223,7 @@ export type CreateFolderRequest = z.infer<typeof CreateFolderRequest>;
 
 export const transcribeUrlRequestBody = z.object({
 	url: z.string(),
-	languageCode: zodLanguageCode,
+	languageCode: InputLanguageCode,
 	translationRequested: z.boolean(),
 	diarizationRequested: z.boolean(),
 });
@@ -225,7 +233,7 @@ export type TranscribeUrlRequestBody = z.infer<typeof transcribeUrlRequestBody>;
 export const transcribeFileRequestBody = z.object({
 	s3Key: z.string(),
 	fileName: z.string(),
-	languageCode: zodLanguageCode,
+	languageCode: InputLanguageCode,
 	translationRequested: z.boolean(),
 	diarizationRequested: z.boolean(),
 });
@@ -263,7 +271,7 @@ export const TranscriptionDynamoItem = z.object({
 	userEmail: z.string(),
 	completedAt: z.optional(z.string()), // dynamodb can't handle dates so we need to use an ISO date
 	isTranslation: z.boolean(),
-	languageCode: z.optional(LanguageCode),
+	languageCode: z.optional(OutputLanguageCode),
 	exportStatuses: z.optional(ExportStatuses),
 });
 
diff --git a/packages/output-handler/src/index.ts b/packages/output-handler/src/index.ts
index 9242e2cf..ed84cee7 100644
--- a/packages/output-handler/src/index.ts
+++ b/packages/output-handler/src/index.ts
@@ -18,7 +18,6 @@ import {
 	TranscriptionOutputFailure,
 	transcriptionOutputIsTranscriptionFailure,
 	TranscriptionDynamoItem,
-	LanguageCode,
 } from '@guardian/transcription-service-common';
 import {
 	MetricsService,
@@ -64,14 +63,6 @@ const handleTranscriptionSuccess = async (
 	metrics: MetricsService,
 	sourceMediaDownloadUrl: string,
 ) => {
-	const languageCode = LanguageCode.safeParse(transcriptionOutput.languageCode);
-	if (!languageCode.success) {
-		logger.error('Failed to parse language code', {
-			languageCode: transcriptionOutput.languageCode,
-		});
-		await metrics.putMetric(FailureMetric);
-		return;
-	}
 	const dynamoItem: TranscriptionDynamoItem = {
 		id: transcriptionOutput.id,
 		originalFilename: transcriptionOutput.originalFilename,
@@ -83,7 +74,7 @@ const handleTranscriptionSuccess = async (
 		userEmail: transcriptionOutput.userEmail,
 		completedAt: new Date().toISOString(),
 		isTranslation: transcriptionOutput.isTranslation,
-		languageCode: languageCode.data,
+		languageCode: transcriptionOutput.languageCode,
 	};
 
 	try {
diff --git a/packages/worker/src/index.ts b/packages/worker/src/index.ts
index 98eb32b8..4075ad7b 100644
--- a/packages/worker/src/index.ts
+++ b/packages/worker/src/index.ts
@@ -17,6 +17,7 @@ import {
 import {
 	DestinationService,
 	OutputBucketKeys,
+	OutputLanguageCode,
 	TranscriptionJob,
 	TranscriptionOutputFailure,
 	type TranscriptionOutputSuccess,
@@ -348,6 +349,11 @@ const pollTranscriptionQueue = async (
 			job.engine === 'whisperx',
 		);
 
+		const languageCode: OutputLanguageCode =
+			job.languageCode === 'auto'
+				? transcriptResult.metadata.detectedLanguageCode
+				: job.languageCode;
+
 		// if we've received an interrupt signal we don't want to perform a half-finished transcript upload/publish as
 		// this may, for example, result in duplicate emails to the user. Here we assume that we can upload some text
 		// files to s3 and make a single request to SNS and SQS within 20 seconds
@@ -385,10 +391,7 @@ const pollTranscriptionQueue = async (
 		const transcriptionOutput: TranscriptionOutputSuccess = {
 			id: job.id,
 			status: 'SUCCESS',
-			languageCode:
-				job.languageCode === 'auto'
-					? transcriptResult.metadata.detectedLanguageCode || 'UNKNOWN'
-					: job.languageCode,
+			languageCode,
 			userEmail: job.userEmail,
 			originalFilename: job.originalFilename,
 			outputBucketKeys,
diff --git a/packages/worker/src/transcribe.ts b/packages/worker/src/transcribe.ts
index 538c2ddf..47a39f03 100644
--- a/packages/worker/src/transcribe.ts
+++ b/packages/worker/src/transcribe.ts
@@ -2,8 +2,10 @@ import path from 'path';
 import { readFile } from '@guardian/transcription-service-backend-common';
 import { logger } from '@guardian/transcription-service-backend-common';
 import {
-	LanguageCode,
+	InputLanguageCode,
+	inputToOutputLanguageCode,
 	languageCodes,
+	OutputLanguageCode,
 	TranscriptionEngine,
 } from '@guardian/transcription-service-common';
 import { runSpawnCommand } from '@guardian/transcription-service-backend-common/src/process';
@@ -21,7 +23,7 @@ export interface Transcripts {
 }
 
 type TranscriptionMetadata = {
-	detectedLanguageCode?: string;
+	detectedLanguageCode: OutputLanguageCode;
 	loadTimeMs?: number;
 	totalTimeMs?: number;
 };
@@ -133,7 +135,7 @@ const getDuration = (ffmpegOutput: string) => {
 
 const runTranscription = async (
 	whisperBaseParams: WhisperBaseParams,
-	languageCode: LanguageCode,
+	languageCode: InputLanguageCode,
 	translate: boolean,
 	whisperX: boolean,
 ) => {
@@ -181,7 +183,7 @@ const runTranscription = async (
 const getLanguageCode = async (
 	whisperBaseParams: WhisperBaseParams,
 	whisperX: boolean,
-): Promise<LanguageCode> => {
+): Promise<InputLanguageCode> => {
 	// whisperx is so slow to start up let's not even bother pre-detecting the language and just let it run detection
 	// for both transcription and translation
 	if (whisperX) {
@@ -214,7 +216,8 @@ const transcribeAndTranslate = async (
 
 		// we only run language detection once,
 		// so need to override the detected language of future whisper runs
-		transcription.metadata.detectedLanguageCode = languageCode;
+		transcription.metadata.detectedLanguageCode =
+			inputToOutputLanguageCode(languageCode);
 		const translation =
 			languageCode === 'en'
 				? null
@@ -241,7 +244,7 @@ const transcribeAndTranslate = async (
 
 export const getTranscriptionText = async (
 	whisperBaseParams: WhisperBaseParams,
-	languageCode: LanguageCode,
+	languageCode: InputLanguageCode,
 	translate: boolean,
 	combineTranscribeAndTranslate: boolean,
 	whisperX: boolean,
@@ -257,11 +260,16 @@ const regexExtract = (text: string, regex: RegExp): string | undefined => {
 	return regexResult ? regexResult[1] : undefined;
 };
 
+const parseLanguageCodeString = (languageCode?: string): OutputLanguageCode =>
+	languageCodes.find((c) => c === languageCode) || 'UNKNOWN';
+
 const extractWhisperXStderrData = (stderr: string): TranscriptionMetadata => {
 	//Detected language: en (0.99) in first 30s of audio...
 	const languageRegex = /Detected language: ([a-zA-Z]{2})/;
 	const detectedLanguageCode = regexExtract(stderr, languageRegex);
-	return { detectedLanguageCode };
+	return {
+		detectedLanguageCode: parseLanguageCodeString(detectedLanguageCode),
+	};
 };
 
 const extractWhisperStderrData = (stderr: string): TranscriptionMetadata => {
@@ -275,7 +283,7 @@ const extractWhisperStderrData = (stderr: string): TranscriptionMetadata => {
 	const loadTime = regexExtract(stderr, loadTimeRegex);
 
 	return {
-		detectedLanguageCode: detectedLanguageCode,
+		detectedLanguageCode: parseLanguageCodeString(detectedLanguageCode),
 		loadTimeMs: loadTime ? parseInt(loadTime) : undefined,
 		totalTimeMs: totalTime ? parseInt(totalTime) : undefined,
 	};
@@ -284,7 +292,7 @@ const extractWhisperStderrData = (stderr: string): TranscriptionMetadata => {
 const whisperParams = (
 	detectLanguageOnly: boolean,
 	file: string,
-	languageCode: LanguageCode = 'auto',
+	languageCode: InputLanguageCode = 'auto',
 	translate: boolean = false,
 ) => {
 	if (detectLanguageOnly) {
@@ -308,7 +316,7 @@ const whisperParams = (
 
 export const runWhisperX = async (
 	whisperBaseParams: WhisperBaseParams,
-	languageCode: LanguageCode,
+	languageCode: InputLanguageCode,
 	translate: boolean,
 ) => {
 	const { wavPath, diarize, stage } = whisperBaseParams;