diff --git a/src/assets/middleware/asset-preprocessing.js b/src/assets/middleware/asset-preprocessing.ts
similarity index 88%
rename from src/assets/middleware/asset-preprocessing.js
rename to src/assets/middleware/asset-preprocessing.ts
index 8bfc0fbc4b76..1a5a1cd6d8c0 100644
--- a/src/assets/middleware/asset-preprocessing.js
+++ b/src/assets/middleware/asset-preprocessing.ts
@@ -1,3 +1,7 @@
+import type { Response, NextFunction } from 'express'
+
+import type { ExtendedRequest } from '@/types'
+
 // This middleware rewrites the URL of requests that contain the
 // portion of `/cb-\d+/`.
 // "cb" stands for "cache bust".
@@ -10,7 +14,11 @@
 
 const regex = /\/cb-\d+\//
 
-export default function assetPreprocessing(req, res, next) {
+export default function assetPreprocessing(
+  req: ExtendedRequest,
+  res: Response,
+  next: NextFunction,
+) {
   if (req.path.startsWith('/assets/')) {
     // We didn't use to have a rule about all image assets must be
     // lower case. So we've exposed things like:
diff --git a/src/frame/middleware/index.ts b/src/frame/middleware/index.ts
index 512e5ffdc914..4ec6baa8c3e7 100644
--- a/src/frame/middleware/index.ts
+++ b/src/frame/middleware/index.ts
@@ -52,7 +52,7 @@ import featuredLinks from '@/landings/middleware/featured-links.js'
 import learningTrack from '@/learning-track/middleware/learning-track.js'
 import next from './next.js'
 import renderPage from './render-page.js'
-import assetPreprocessing from '@/assets/middleware/asset-preprocessing.js'
+import assetPreprocessing from '@/assets/middleware/asset-preprocessing'
 import archivedAssetRedirects from '@/archives/middleware/archived-asset-redirects.js'
 import favicons from './favicons.js'
 import setStaticAssetCaching from '@/assets/middleware/static-asset-caching.js'