diff --git a/.prettierignore b/.prettierignore
index bb611591d0..0fdd31c1e0 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -10,7 +10,7 @@ pnpm-lock.yaml
 /web/third/marked/*
 !/web/third/marked/lib
 /web/third/marked/lib/*
-!/web/third/marked/lib/marked.d.ts
+!/web/third/marked/lib/marked.d.cts
 /zerver/tests/fixtures
 /zerver/webhooks/*/doc.md
 /zerver/webhooks/github/githubsponsors.md
diff --git a/docs/subsystems/markdown.md b/docs/subsystems/markdown.md
index 2589a20986..48d0b7f772 100644
--- a/docs/subsystems/markdown.md
+++ b/docs/subsystems/markdown.md
@@ -102,7 +102,7 @@ places:
 
 - The backend Markdown processor (`zerver/lib/markdown/__init__.py`).
 - The frontend Markdown processor (`web/src/markdown.ts` and sometimes
-  `web/third/marked/lib/marked.js`), or `markdown.contains_backend_only_syntax` if
+  `web/third/marked/lib/marked.cjs`), or `markdown.contains_backend_only_syntax` if
   your changes won't be supported in the frontend processor.
 - If desired, the typeahead logic in `web/src/composebox_typeahead.ts`.
 - The test suite, probably via adding entries to `zerver/tests/fixtures/markdown_test_cases.json`.
diff --git a/web/src/markdown.ts b/web/src/markdown.ts
index 9461209e59..471f9c7461 100644
--- a/web/src/markdown.ts
+++ b/web/src/markdown.ts
@@ -5,13 +5,13 @@ import assert from "minimalistic-assert";
 import type {Template} from "url-template";
 
 import * as fenced_code from "../shared/src/fenced_code.ts";
-import marked from "../third/marked/lib/marked.js";
-import type {LinkifierMatch, ParseOptions, RegExpOrStub} from "../third/marked/lib/marked.js";
+import marked from "../third/marked/lib/marked.cjs";
+import type {LinkifierMatch, ParseOptions, RegExpOrStub} from "../third/marked/lib/marked.cjs";
 
 // This contains zulip's frontend Markdown implementation; see
 // docs/subsystems/markdown.md for docs on our Markdown syntax.  The other
 // main piece in rendering Markdown client-side is
-// web/third/marked/lib/marked.js, which we have significantly
+// web/third/marked/lib/marked.cjs, which we have significantly
 // modified from the original implementation.
 
 // Docs: https://zulip.readthedocs.io/en/latest/subsystems/markdown.html
diff --git a/web/third/marked/lib/marked.js b/web/third/marked/lib/marked.cjs
similarity index 100%
rename from web/third/marked/lib/marked.js
rename to web/third/marked/lib/marked.cjs
diff --git a/web/third/marked/lib/marked.d.ts b/web/third/marked/lib/marked.d.cts
similarity index 100%
rename from web/third/marked/lib/marked.d.ts
rename to web/third/marked/lib/marked.d.cts