diff --git a/gui/src/components/use-main-device-reauth.ts b/gui/src/components/use-main-device-reauth.ts
index 626e004a5c1..44d18b9645f 100644
--- a/gui/src/components/use-main-device-reauth.ts
+++ b/gui/src/components/use-main-device-reauth.ts
@@ -181,6 +181,12 @@ export function useMainDeviceReauth(apiBase: string, onCompleted: () => void) {
         const dto = await res.json().catch(() => ({})) as FlowDto;
         if (!isCurrent() || flowRef.current !== flowId) return;
         if (!res.ok) {
+          if (res.status === 404 && dto.code === "unknown_flow") {
+            stopPolling();
+            flowRef.current = null;
+            setState({ phase: "failed", code: "request_failed" });
+            return;
+          }
           // Ownership continues from the Cancel click, including while DELETE
           // is unresolved. Never offer a replacement POST during that window,
           // and keep the existing poll cadence so a later terminal status remains observable.
diff --git a/gui/tests/main-device-reauth-ownership.test.tsx b/gui/tests/main-device-reauth-ownership.test.tsx
index 917cb5f80d1..e90315560b3 100644
--- a/gui/tests/main-device-reauth-ownership.test.tsx
+++ b/gui/tests/main-device-reauth-ownership.test.tsx
@@ -315,6 +315,17 @@ for (const failure of ["network", "http", "nonterminal"] as const) {
   });
 }
 
+test("unknown flow status stops polling after a failed cancellation", async () => {
+  await mount();
+  await beginFlow("A");
+  await invoke(() => hook.cancel());
+  await reply(take("DELETE", "A"), { code: "unavailable" }, 503);
+  await act(async () => { for (const wake of sleepers.splice(0)) wake(); });
+  await reply(take("GET", "A"), { code: "unknown_flow" }, 404);
+  expect(hook.state).toEqual({ phase: "failed", code: "request_failed" });
+  expect(sleepers).toHaveLength(0);
+});
+
 test("two successful cancellation replies complete the same flow only once", async () => {
   await mount();
   await beginFlow("A");