diff --git a/src/cli/update-restart-child.ts b/src/cli/update-restart-child.ts
index 817364ea038..2f1e7f4aedf 100644
--- a/src/cli/update-restart-child.ts
+++ b/src/cli/update-restart-child.ts
@@ -18,8 +18,11 @@ function parseMarker(raw: string): UpdateRestartChildMarker {
     || value.version === "0.0.0" || !parseStrictSemver(value.version) || !value.home
     || !Number.isSafeInteger(value.home.revision)) throw new Error("update_restart_child_marker_invalid");
   for (const directory of [value.home.config, value.home.codex]) {
+    // Windows reports 64-bit NTFS file ids (MFT sequence in the high 16 bits) as doubles above
+    // 2^53. Parent and child read them through the same stat API, so any finite integer is a
+    // faithful identity token; assertUpdateRestartHome still compares path, dev and ino exactly.
     if (!directory || typeof directory.path !== "string" || !directory.path
-      || !Number.isSafeInteger(directory.dev) || !Number.isSafeInteger(directory.ino)) {
+      || !Number.isInteger(directory.dev) || !Number.isInteger(directory.ino)) {
       throw new Error("update_restart_child_marker_invalid");
     }
   }
diff --git a/tests/cli/cli-update-restart-home.test.ts b/tests/cli/cli-update-restart-home.test.ts
index e82324b659b..5f73747fd7a 100644
--- a/tests/cli/cli-update-restart-home.test.ts
+++ b/tests/cli/cli-update-restart-home.test.ts
@@ -50,6 +50,27 @@ test("busy child lease leaves config bytes, permissions and files unchanged", ()
   expect({ bytes: readFileSync(configPath, "utf8"), mode: statSync(configPath).mode, files: readdirSync(h.config) }).toEqual(before);
 });
 
+test("NTFS file ids above 2^53 are admitted as home identity", () => {
+  // Windows runners hand out directory ids with the MFT sequence in the high bits; the marker must
+  // not depend on which id a temp directory happens to receive.
+  const h = home();
+  const captured = readUpdateRestartHome();
+  const large = { ...captured, config: { ...captured.config, ino: 2 ** 60 + 4096 }, codex: { ...captured.codex, dev: 2 ** 56 } };
+  const marker = { home: large, version: "2.77.0", port: 10100, hostname: "127.0.0.1", deadlineAt: Date.now() + 5000 };
+  writeFileSync(join(h.config, "config.json"), '{"hostname":"127.0.0.1"}\n');
+  const seen: unknown[] = [];
+  expect(() => admitUpdateRestartChild(["start", "--port", "10100"], {
+    env: { [UPDATE_RESTART_CHILD_ENV]: JSON.stringify(marker) }, version: () => "2.77.0",
+    checkHome: home => { seen.push(home); }, checkState: () => {},
+    acquire: () => { throw new Error("lease busy"); },
+  })).toThrow("lease busy");
+  expect(seen).toEqual([large]);
+  for (const ino of [Number.NaN, Number.POSITIVE_INFINITY, 1.5]) {
+    const bad = JSON.stringify({ ...marker, home: { ...large, config: { ...large.config, ino } } });
+    expect(() => admitUpdateRestartChild(["start", "--port", "10100"], { env: { [UPDATE_RESTART_CHILD_ENV]: bad } })).toThrow("update_restart_child_marker_invalid");
+  }
+});
+
 test("production parent guard rejects client and hostname drift before stop", () => {
   const h = home(); const config = join(h.config, "config.json");
   writeFileSync(config, JSON.stringify({ hostname: "127.0.0.1" }));