diff --git a/apps/web/src/components/ChatMarkdown.tsx b/apps/web/src/components/ChatMarkdown.tsx
index 985e943cb39..a61c6e25893 100644
--- a/apps/web/src/components/ChatMarkdown.tsx
+++ b/apps/web/src/components/ChatMarkdown.tsx
@@ -128,6 +128,10 @@ const highlightedCodeCache = new LRUCache<string>(
   MAX_HIGHLIGHT_CACHE_MEMORY_BYTES,
 );
 
+const WINDOWS_DRIVE_LINK_PROTOCOLS = Array.from(
+  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz",
+);
+
 function findTaskListMarkerOffset(markdown: string, listItemStart: number): number | null {
   const firstLineEnd = markdown.indexOf("\n", listItemStart);
   const firstLine = markdown.slice(
@@ -147,7 +151,10 @@ const CHAT_MARKDOWN_SANITIZE_SCHEMA = {
   },
   protocols: {
     ...defaultSchema.protocols,
-    href: [...(defaultSchema.protocols?.href ?? []), "file"],
+    // rehype-sanitize runs before react-markdown's urlTransform. A Windows
+    // drive letter looks like a protocol (`C:`), so allow drive letters here;
+    // urlTransform only preserves values with a drive-path shape afterward.
+    href: [...(defaultSchema.protocols?.href ?? []), "file", ...WINDOWS_DRIVE_LINK_PROTOCOLS],
   },
 } satisfies Parameters<typeof rehypeSanitize>[0];
 
diff --git a/apps/web/src/markdown-links.test.ts b/apps/web/src/markdown-links.test.ts
index 9fc29613867..cdc1cb799d3 100644
--- a/apps/web/src/markdown-links.test.ts
+++ b/apps/web/src/markdown-links.test.ts
@@ -21,17 +21,39 @@ describe("rewriteMarkdownFileUriHref", () => {
   });
 
   it("normalizes file uri hrefs for windows drive paths", () => {
+    const canonicalHref = "/D:/Programme/t3code/apps/web/src/components/chat/OpenInPicker.tsx#L69";
     expect(
       rewriteMarkdownFileUriHref(
         "file:///D:/Programme/t3code/apps/web/src/components/chat/OpenInPicker.tsx#L69",
       ),
-    ).toBe("D:/Programme/t3code/apps/web/src/components/chat/OpenInPicker.tsx#L69");
+    ).toBe(canonicalHref);
+    expect(rewriteMarkdownFileUriHref(canonicalHref)).toBe(canonicalHref);
   });
 
   it("unwraps angle-bracketed file uri hrefs", () => {
     expect(
       rewriteMarkdownFileUriHref(" <file:///D:/Programme/t3code/apps/web/src/markdown-links.ts> "),
-    ).toBe("D:/Programme/t3code/apps/web/src/markdown-links.ts");
+    ).toBe("/D:/Programme/t3code/apps/web/src/markdown-links.ts");
+  });
+
+  it("canonicalizes windows drive hrefs for the custom markdown file renderer", () => {
+    expect(rewriteMarkdownFileUriHref("C:/Users/mike/project/src/main.ts:42")).toBe(
+      "/C:/Users/mike/project/src/main.ts:42",
+    );
+    expect(rewriteMarkdownFileUriHref("C:\\Users\\mike\\project\\src\\main.ts:42")).toBe(
+      "/C:/Users/mike/project/src/main.ts:42",
+    );
+    expect(rewriteMarkdownFileUriHref("C:%5CUsers%5Cmike%5Cproject%5Csrc%5Cmain.ts:42")).toBe(
+      "/C:/Users/mike/project/src/main.ts:42",
+    );
+    expect(rewriteMarkdownFileUriHref("C://Users/mike/project/src/main.ts:42")).toBe(
+      "/C:/Users/mike/project/src/main.ts:42",
+    );
+  });
+
+  it("ignores non-file hrefs", () => {
+    expect(rewriteMarkdownFileUriHref("https://example.com/docs")).toBeNull();
+    expect(rewriteMarkdownFileUriHref("x:command")).toBeNull();
   });
 });
 
diff --git a/apps/web/src/markdown-links.ts b/apps/web/src/markdown-links.ts
index a6dba941b8a..8f299d14d0a 100644
--- a/apps/web/src/markdown-links.ts
+++ b/apps/web/src/markdown-links.ts
@@ -103,9 +103,18 @@ function parseFileUrlHref(
 export function rewriteMarkdownFileUriHref(href: string | undefined): string | null {
   if (!href) return null;
   const normalizedHref = normalizeMarkdownLinkDestination(href);
+  // Markdown parsing can encode backslashes or duplicate the drive separator.
+  const windowsDriveHref = normalizedHref
+    .replaceAll(/%5c/gi, "/")
+    .replaceAll(/\\/g, "/")
+    .replace(/^\/?([A-Za-z]):\/+/, "/$1:/");
+  // A leading slash keeps the drive letter from being treated as a URL scheme.
+  if (/^\/[A-Za-z]:\//.test(windowsDriveHref)) return windowsDriveHref;
+
   const target = parseFileUrlHref(normalizedHref, { decodePath: false });
   if (!target) return null;
-  return `${target.path}${target.hash}`;
+  const path = WINDOWS_DRIVE_PATH_PATTERN.test(target.path) ? `/${target.path}` : target.path;
+  return `${path}${target.hash}`;
 }
 
 function looksLikePosixFilesystemPath(path: string): boolean {