diff --git a/oidc-proxy/README.md b/oidc-proxy/README.md
index 361eb99dfb..8f442125f0 100644
--- a/oidc-proxy/README.md
+++ b/oidc-proxy/README.md
@@ -28,7 +28,7 @@ Edit `wrangler.toml` for your upstream:
 |---|---|
 | `OIDC_ISSUER` | `https://token.actions.githubusercontent.com` |
 | `OIDC_AUDIENCE` | The audience your workflow requests (e.g. `goose-oidc-proxy`) |
-| `MAX_TOKEN_AGE_SECONDS` | Max age of OIDC token in seconds (default: `1200` = 20 min) |
+| `MAX_TOKEN_AGE_SECONDS` | Operator-configured upper bound on `iat` age in seconds (default: `1200` = 20 min). Applied **in addition to** the IdP's `exp` claim, never as a replacement. |
 | `MAX_REQUESTS_PER_TOKEN` | Max requests per OIDC token (default: `200`) |
 | `RATE_LIMIT_PER_SECOND` | Max requests per second per token (default: `2`) |
 | `ALLOWED_REPOS` | *(optional)* Comma-separated `owner/repo` list |
@@ -108,4 +108,9 @@ Both limits are enforced atomically — the Durable Object processes one request
 
 ## Token age vs expiry
 
-GitHub OIDC tokens expire after ~5 minutes. For longer-running jobs, set `MAX_TOKEN_AGE_SECONDS` to allow recently-expired tokens. When set, the proxy checks the token's `iat` (issued-at) claim instead of `exp`.
+The proxy enforces **both** gates and a token must pass each:
+
+1. The IdP's `exp` claim (always enforced).
+2. The operator's `MAX_TOKEN_AGE_SECONDS` cap on `iat`, when configured (default `1200`s = 20 min).
+
+`MAX_TOKEN_AGE_SECONDS` is a stricter upper bound *on top of* `exp` — it cannot extend a token past its `exp`. For workflows longer than the IdP's token lifetime (GitHub OIDC issues `exp = iat + 300` ≈ 5 min), refresh the OIDC token rather than relying on `MAX_TOKEN_AGE_SECONDS` to accept expired tokens.
diff --git a/oidc-proxy/src/index.js b/oidc-proxy/src/index.js
index a942a95e53..8188a52852 100644
--- a/oidc-proxy/src/index.js
+++ b/oidc-proxy/src/index.js
@@ -190,17 +190,16 @@ async function verifyOidcToken(token, env) {
     const header = decodeJwtPart(headerB64);
     const payload = decodeJwtPart(payloadB64);
 
+    if (!payload.exp || payload.exp < Date.now() / 1000) {
+      return { valid: false, reason: "Token expired" };
+    }
     if (env.MAX_TOKEN_AGE_SECONDS && payload.iat) {
-      const age = Date.now() / 1000 - payload.iat;
+      const age = Math.floor(Date.now() / 1000) - payload.iat;
       if (age > parseInt(env.MAX_TOKEN_AGE_SECONDS, 10)) {
         return { valid: false, reason: "Token too old" };
       }
     }
 
-    if (!payload.exp || payload.exp < Date.now() / 1000) {
-      return { valid: false, reason: "Token expired" };
-    }
-
     const expectedIssuer = env.OIDC_ISSUER.replace(/\/$/, "");
     const actualIssuer = (payload.iss || "").replace(/\/$/, "");
     if (actualIssuer !== expectedIssuer) {
diff --git a/oidc-proxy/test/index.test.js b/oidc-proxy/test/index.test.js
index 1a1d0b8bbf..41de473856 100644
--- a/oidc-proxy/test/index.test.js
+++ b/oidc-proxy/test/index.test.js
@@ -206,6 +206,62 @@ describe("rejects invalid requests", () => {
     expect(response.status).toBe(401);
     expect((await response.json()).error).toBe("Token too old");
   });
+
+  it("age cap fires independently of exp (iat past cap, exp still valid)", async () => {
+    const now = Math.floor(Date.now() / 1000);
+    const token = await createSignedJwt(
+      validPayload({ iat: now - 1500, exp: now + 300 }),
+    );
+    const request = new Request("https://proxy.example.com/v1/messages", {
+      headers: { "x-api-key": token },
+    });
+    const ctx = createExecutionContext();
+    const response = await worker.fetch(request, testEnv(), ctx);
+    await waitOnExecutionContext(ctx);
+
+    expect(response.status).toBe(401);
+    expect((await response.json()).error).toBe("Token too old");
+  });
+
+  it("rejects expired token even when MAX_TOKEN_AGE_SECONDS is set", async () => {
+    const now = Math.floor(Date.now() / 1000);
+    const token = await createSignedJwt(
+      validPayload({ iat: now - 600, exp: now - 300 }),
+    );
+    const request = new Request("https://proxy.example.com/v1/messages", {
+      method: "POST",
+      headers: { "x-api-key": token, "Content-Type": "application/json" },
+      body: JSON.stringify({}),
+    });
+    const ctx = createExecutionContext();
+    const response = await worker.fetch(request, testEnv(), ctx);
+    await waitOnExecutionContext(ctx);
+
+    expect(response.status).toBe(401);
+    expect((await response.json()).error).toBe("Token expired");
+  });
+
+  it("rejects expired token when MAX_TOKEN_AGE_SECONDS is unset", async () => {
+    const now = Math.floor(Date.now() / 1000);
+    const token = await createSignedJwt(
+      validPayload({ iat: now - 600, exp: now - 300 }),
+    );
+    const request = new Request("https://proxy.example.com/v1/messages", {
+      method: "POST",
+      headers: { "x-api-key": token, "Content-Type": "application/json" },
+      body: JSON.stringify({}),
+    });
+    const ctx = createExecutionContext();
+    const response = await worker.fetch(
+      request,
+      testEnv({ MAX_TOKEN_AGE_SECONDS: undefined }),
+      ctx,
+    );
+    await waitOnExecutionContext(ctx);
+
+    expect(response.status).toBe(401);
+    expect((await response.json()).error).toBe("Token expired");
+  });
 });
 
 describe("proxies valid requests", () => {