diff --git a/src/index.ts b/src/index.ts
index 23fe8ea..fbd231d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -301,7 +301,7 @@ export function stringifySetCookie(
   let str = cookie.name + "=" + value;
 
   if (cookie.maxAge !== undefined) {
-    if (!Number.isInteger(cookie.maxAge)) {
+    if (!Number.isSafeInteger(cookie.maxAge)) {
       throw new TypeError(`option maxAge is invalid: ${cookie.maxAge}`);
     }
 
diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index f4e9cd4..e709e63 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -181,6 +181,7 @@ describe("cookie.stringifySetCookie", () => {
       ["non-number", "buzz"],
       ["Infinity", Infinity],
       ["non-integer", 3.14],
+      ["unsafe integer", 1e21],
     ])("should throw when maxAge is %s", (_label, maxAge) => {
       expect(() =>
         stringifySetCookie({ name: "foo", value: "bar", maxAge } as any),