diff --git a/app/api/keystatic/[...params]/route.ts b/app/api/keystatic/[...params]/route.ts
index b6cc67d4a..ee352340f 100644
--- a/app/api/keystatic/[...params]/route.ts
+++ b/app/api/keystatic/[...params]/route.ts
@@ -1,32 +1,10 @@
-import { isNonEmptyString } from "@acdh-oeaw/lib";
 import { makeRouteHandler } from "@keystatic/next/route-handler";
 
 import config from "@/keystatic.config";
+import { rewriteUrl } from "@/lib/rewrite-url";
 
 const { GET: _GET, POST: _POST } = makeRouteHandler({ config });
 
-/**
- * @see https://github.com/Thinkmill/keystatic/issues/978#issuecomment-2005730530
- * @see https://github.com/Thinkmill/keystatic/issues/1022
- */
-function rewriteUrl(request: Request) {
-	const forwardedHost = request.headers.get("x-forwarded-host");
-	const forwardedProto = request.headers.get("x-forwarded-proto");
-	const forwardedPort = request.headers.get("x-forwarded-port");
-
-	if (isNonEmptyString(forwardedHost) && isNonEmptyString(forwardedProto)) {
-		const url = new URL(request.url);
-
-		url.hostname = forwardedHost;
-		url.protocol = forwardedProto;
-		url.port = forwardedPort ?? "";
-
-		return new Request(url, request);
-	}
-
-	return request;
-}
-
 export function GET(request: Request) {
 	return _GET(rewriteUrl(request));
 }
diff --git a/app/api/preview/start/route.ts b/app/api/preview/start/route.ts
index 1a185bdc0..7e0af0a65 100644
--- a/app/api/preview/start/route.ts
+++ b/app/api/preview/start/route.ts
@@ -1,7 +1,10 @@
 import { cookies, draftMode } from "next/headers";
 import { redirect } from "next/navigation";
 
-export function GET(request: Request): Response {
+import { rewriteUrl } from "@/lib/rewrite-url";
+
+export function GET(_request: Request): Response {
+	const request = rewriteUrl(_request);
 	const url = new URL(request.url);
 	const params = url.searchParams;
 
@@ -18,5 +21,5 @@ export function GET(request: Request): Response {
 	toUrl.protocol = url.protocol;
 	toUrl.host = url.host;
 
-	redirect(toUrl.toString());
+	redirect(String(toUrl));
 }
diff --git a/lib/rewrite-url.ts b/lib/rewrite-url.ts
new file mode 100644
index 000000000..ceab0e980
--- /dev/null
+++ b/lib/rewrite-url.ts
@@ -0,0 +1,23 @@
+import { isNonEmptyString } from "@acdh-oeaw/lib";
+
+/**
+ * @see https://github.com/Thinkmill/keystatic/issues/978#issuecomment-2005730530
+ * @see https://github.com/Thinkmill/keystatic/issues/1022
+ */
+export function rewriteUrl(request: Request): Request {
+	const forwardedHost = request.headers.get("x-forwarded-host");
+	const forwardedProto = request.headers.get("x-forwarded-proto");
+	const forwardedPort = request.headers.get("x-forwarded-port");
+
+	if (isNonEmptyString(forwardedHost) && isNonEmptyString(forwardedProto)) {
+		const url = new URL(request.url);
+
+		url.hostname = forwardedHost;
+		url.protocol = forwardedProto;
+		url.port = forwardedPort ?? "";
+
+		return new Request(url, request);
+	}
+
+	return request;
+}