diff --git a/src/app/projects/[projectId]/work-orders/[workOrderId]/ids.ts b/src/app/projects/[projectId]/work-orders/[workOrderId]/ids.ts
new file mode 100644
index 00000000..470722fd
--- /dev/null
+++ b/src/app/projects/[projectId]/work-orders/[workOrderId]/ids.ts
@@ -0,0 +1,18 @@
+/**
+ * Path-segment parsing for the work-order detail route (issue #422).
+ *
+ * Kept out of `page.tsx` because Next.js rejects any non-default export from a
+ * page module beyond its handful of allowed fields — a helper exported there
+ * fails the build. Mirrors `parseProjectId` in `../../../guards`.
+ */
+
+/**
+ * Parse a `[workOrderId]` path segment into the bigint PK it addresses, or null
+ * for anything that is not a bare positive integer — so a junk segment becomes
+ * a 404 rather than a Drizzle error.
+ */
+export function parseWorkOrderId(workOrderId: string): bigint | null {
+  if (!/^\d+$/.test(workOrderId)) return null;
+  const parsed = BigInt(workOrderId);
+  return parsed > 0n ? parsed : null;
+}
diff --git a/src/app/projects/[projectId]/work-orders/[workOrderId]/page.test.tsx b/src/app/projects/[projectId]/work-orders/[workOrderId]/page.test.tsx
index 5111b09a..54c8d7d9 100644
--- a/src/app/projects/[projectId]/work-orders/[workOrderId]/page.test.tsx
+++ b/src/app/projects/[projectId]/work-orders/[workOrderId]/page.test.tsx
@@ -39,7 +39,8 @@ vi.mock("next/link", () => ({
   }) => <a href={href}>{children}</a>,
 }));
 
-import WorkOrderDetailPage, { parseWorkOrderId } from "./page";
+import WorkOrderDetailPage from "./page";
+import { parseWorkOrderId } from "./ids";
 
 const CLIENT_ORG = "11111111-1111-1111-1111-111111111111";
 const CONTRACTOR_ORG = "22222222-2222-2222-2222-222222222222";
diff --git a/src/app/projects/[projectId]/work-orders/[workOrderId]/page.tsx b/src/app/projects/[projectId]/work-orders/[workOrderId]/page.tsx
index 6a6641e8..d3dbbecf 100644
--- a/src/app/projects/[projectId]/work-orders/[workOrderId]/page.tsx
+++ b/src/app/projects/[projectId]/work-orders/[workOrderId]/page.tsx
@@ -15,6 +15,7 @@ import {
   WorkOrderHeader,
 } from "./components/WorkOrderDetailPanels";
 import { EvidenceUploadSlot, StageUpdateSlot } from "./components/ActionSlots";
+import { parseWorkOrderId } from "./ids";
 
 export const metadata = {
   title: "Work order | Ara",
@@ -93,14 +94,3 @@ export default async function WorkOrderDetailPage(props: {
     </div>
   );
 }
-
-/**
- * Parse a `[workOrderId]` path segment into the bigint PK it addresses, or null
- * for anything that is not a bare positive integer — so a junk segment becomes
- * a 404 rather than a Drizzle error. Mirrors `parseProjectId` in the guards.
- */
-export function parseWorkOrderId(workOrderId: string): bigint | null {
-  if (!/^\d+$/.test(workOrderId)) return null;
-  const parsed = BigInt(workOrderId);
-  return parsed > 0n ? parsed : null;
-}