diff --git a/packages/web/src/components/codeMirrorWrapper.tsx b/packages/web/src/components/codeMirrorWrapper.tsx
index 1ac346502a..eb551a66da 100644
--- a/packages/web/src/components/codeMirrorWrapper.tsx
+++ b/packages/web/src/components/codeMirrorWrapper.tsx
@@ -27,9 +27,11 @@ export type SourceHighlight = {
   type: 'running' | 'paused' | 'error';
 };
 
+export type Language = 'javascript' | 'python' | 'java' | 'csharp';
+
 export interface SourceProps {
   text: string;
-  language: string;
+  language: Language;
   readOnly: boolean;
   // 1-based
   highlight?: SourceHighlight[];
diff --git a/packages/web/src/components/source.tsx b/packages/web/src/components/source.tsx
index cae68a8451..5b0bd7c403 100644
--- a/packages/web/src/components/source.tsx
+++ b/packages/web/src/components/source.tsx
@@ -16,6 +16,7 @@
 
 import * as React from 'react';
 import './codeMirrorWrapper.css';
+import type { Language } from './codeMirrorWrapper';
 import { CodeMirrorWrapper } from './codeMirrorWrapper';
 
 export type SourceHighlight = {
@@ -25,7 +26,7 @@ export type SourceHighlight = {
 
 export interface SourceProps {
   text: string;
-  language: string;
+  language: Language;
   // 1-based
   highlight?: SourceHighlight[];
   revealLine?: number;