diff --git a/.changeset/silent-refresh-auth-server-issuer.md b/.changeset/silent-refresh-auth-server-issuer.md
new file mode 100644
index 0000000..0e8818b
--- /dev/null
+++ b/.changeset/silent-refresh-auth-server-issuer.md
@@ -0,0 +1,8 @@
+---
+"@seamless-auth/core": patch
+"@seamless-auth/express": patch
+"@seamless-auth/fastify": patch
+"@seamless-auth/nextjs": patch
+---
+
+Check a silently refreshed access token against `authServerIssuer`. The silent refresh in `ensureCookies` now verifies the token it returns, but it checked `iss` against `authServerUrl` even when `authServerIssuer` was set, so an app reaching the auth server at another URL (the local Docker stack from the host) answered 401 on every silent refresh and signed the user out. `EnsureCookiesOptions` and the Express `createEnsureCookiesMiddleware` take an optional `authServerIssuer`, and the adapters pass their configured one.
diff --git a/packages/core/src/ensureCookies.ts b/packages/core/src/ensureCookies.ts
index 48cdad5..8cbae87 100644
--- a/packages/core/src/ensureCookies.ts
+++ b/packages/core/src/ensureCookies.ts
@@ -2,6 +2,7 @@ import { verifyCookieJwt } from "./verifyCookieJwt.js";
 import type { ResultFailure } from "./result.js";
 import { refreshAccessToken } from "./refreshAccessToken.js";
 import { assertSecrets } from "./validateSecrets.js";
+import type { AuthServerIssuerOption } from "./authServerIssuer.js";
 import {
   issueSessionCookies,
   type UpstreamSessionResponse,
@@ -43,7 +44,7 @@ export interface EnsureCookiesResult extends ResultFailure {
   clearCookies?: string[];
 }
 
-export interface EnsureCookiesOptions {
+export interface EnsureCookiesOptions extends AuthServerIssuerOption {
   authServerUrl: string;
   cookieDomain?: string;
   accessCookieName: string;
@@ -271,6 +272,7 @@ async function refreshRequiredCookie(
       {
         authServerUrl: opts.authServerUrl,
         audience: opts.accessTokenAudience || opts.authServerUrl,
+        authServerIssuer: opts.authServerIssuer,
         accessCookieName: cookieName,
         refreshCookieName: opts.refreshCookieName,
         cookieDomain: opts.cookieDomain,
diff --git a/packages/core/tests/ensureCookies.test.js b/packages/core/tests/ensureCookies.test.js
index 43a2d33..c1d519c 100644
--- a/packages/core/tests/ensureCookies.test.js
+++ b/packages/core/tests/ensureCookies.test.js
@@ -294,6 +294,7 @@ describe("ensureCookies", () => {
         "new-access",
         "https://auth.example.com",
         "https://app.example.com",
+        undefined,
       );
     });
 
@@ -306,6 +307,25 @@ describe("ensureCookies", () => {
         "new-access",
         "https://auth.example.com",
         "https://auth.example.com",
+        undefined,
+      );
+    });
+
+    it("verifies against the configured auth server issuer", async () => {
+      verifySignedAuthResponseMock.mockResolvedValue({ sub: "user-123" });
+
+      await silentRefresh({
+        ...BASE_OPTS,
+        authServerUrl: "http://localhost:5312",
+        authServerIssuer: "http://auth:5312",
+        accessTokenAudience: "http://auth:5312",
+      });
+
+      expect(verifySignedAuthResponseMock).toHaveBeenCalledWith(
+        "new-access",
+        "http://localhost:5312",
+        "http://auth:5312",
+        "http://auth:5312",
       );
     });
 
diff --git a/packages/express/src/createServer.ts b/packages/express/src/createServer.ts
index 3927fb8..8f0cb2c 100644
--- a/packages/express/src/createServer.ts
+++ b/packages/express/src/createServer.ts
@@ -326,6 +326,7 @@ export function createSeamlessAuthServer(
       issuer: SERVICE_TOKEN_ISSUER,
       audience: SERVICE_TOKEN_AUDIENCE,
       accessTokenAudience: resolvedOpts.audience,
+      authServerIssuer: resolvedOpts.authServerIssuer,
       keyId: resolvedOpts.jwksKid,
       resolveClientIp: resolvedOpts.resolveClientIp,
     }),
diff --git a/packages/express/src/middleware/ensureCookies.ts b/packages/express/src/middleware/ensureCookies.ts
index 56267df..6be61d9 100644
--- a/packages/express/src/middleware/ensureCookies.ts
+++ b/packages/express/src/middleware/ensureCookies.ts
@@ -30,6 +30,12 @@ export interface EnsureCookiesMiddlewareOptions {
    * refreshed token is verified against. Defaults to `authServerUrl`.
    */
   accessTokenAudience?: string;
+  /**
+   * Expected `iss` on a silently refreshed access token, when the auth server
+   * signs under a different issuer from `authServerUrl`. Defaults to
+   * `authServerUrl`.
+   */
+  authServerIssuer?: string;
   keyId: string;
   resolveClientIp?: ClientIpResolver;
 }
@@ -68,6 +74,7 @@ export function createEnsureCookiesMiddleware(
         issuer: opts.issuer,
         audience: opts.audience,
         accessTokenAudience: opts.accessTokenAudience,
+        authServerIssuer: opts.authServerIssuer,
         keyId: opts.keyId,
         forwardedClientIp: buildForwardedClientIp(req, opts.resolveClientIp),
         forwardedUserAgent: buildForwardedUserAgent(req),
diff --git a/packages/express/tests/ensureCookies.middleware.test.js b/packages/express/tests/ensureCookies.middleware.test.js
index 8d43984..b3c27af 100644
--- a/packages/express/tests/ensureCookies.middleware.test.js
+++ b/packages/express/tests/ensureCookies.middleware.test.js
@@ -78,11 +78,11 @@ describe("createEnsureCookiesMiddleware silent refresh", () => {
     return server;
   }
 
-  async function refreshWithTokenFor(audience, options, refreshToken) {
+  async function refreshWithTokenFor(audience, options, refreshToken, issuer = AUTH) {
     const token = jwt.sign({ sub: "user-123", typ: "access", sid: "s-1" }, privateKey, {
       algorithm: "RS256",
       keyid: "k1",
-      issuer: AUTH,
+      issuer,
       audience,
       expiresIn: "5m",
     });
@@ -131,4 +131,32 @@ describe("createEnsureCookiesMiddleware silent refresh", () => {
     expect(res.status).toBe(401);
     expect(res.headers["set-cookie"].join(";")).not.toMatch(/access=ey/);
   });
+
+  // On the local Docker stack the auth server signs as http://auth:5312 while
+  // the app reaches it at authServerUrl (fells-code/seamless-cli#224).
+  it("verifies the refreshed token against authServerIssuer", async () => {
+    const res = await refreshWithTokenFor(
+      "http://auth:5312",
+      { accessTokenAudience: "http://auth:5312", authServerIssuer: "http://auth:5312" },
+      "opaque-3",
+      "http://auth:5312",
+    );
+
+    expect(res.status).toBe(200);
+    expect(res.body).toMatchObject({ sub: "user-123", sessionId: "s-1" });
+  });
+
+  it("refuses a refreshed token from an issuer other than the expected one", async () => {
+    const spy = jest.spyOn(console, "error").mockImplementation(() => {});
+    const res = await refreshWithTokenFor(
+      "http://auth:5312",
+      { accessTokenAudience: "http://auth:5312" },
+      "opaque-4",
+      "http://auth:5312",
+    );
+    spy.mockRestore();
+
+    expect(res.status).toBe(401);
+    expect(res.headers["set-cookie"].join(";")).not.toMatch(/access=ey/);
+  });
 });
diff --git a/packages/fastify/src/hooks/ensureCookies.ts b/packages/fastify/src/hooks/ensureCookies.ts
index 12d5dd0..ab6e56d 100644
--- a/packages/fastify/src/hooks/ensureCookies.ts
+++ b/packages/fastify/src/hooks/ensureCookies.ts
@@ -70,6 +70,7 @@ export function createEnsureCookiesHook(opts: ResolvedOptions, prefix: string) {
         issuer: SERVICE_TOKEN_ISSUER,
         audience: SERVICE_TOKEN_AUDIENCE,
         accessTokenAudience: opts.audience,
+        authServerIssuer: opts.authServerIssuer,
         keyId: opts.jwksKid,
         forwardedClientIp: buildForwardedClientIp(req, opts.resolveClientIp),
         forwardedUserAgent: buildForwardedUserAgent(req),
diff --git a/packages/fastify/tests/issuer.parity.test.js b/packages/fastify/tests/issuer.parity.test.js
index 03e6737..89268e8 100644
--- a/packages/fastify/tests/issuer.parity.test.js
+++ b/packages/fastify/tests/issuer.parity.test.js
@@ -93,6 +93,19 @@ async function mockUpstream(issuer) {
         refreshTtl: 2592000,
       });
     }
+    if (href === `${AUTH}/refresh`) {
+      return Response.json({
+        sub: "user-123",
+        token: access,
+        refreshToken: "refresh-2",
+        roles: ["athlete"],
+        ttl: 1800,
+        refreshTtl: 2592000,
+      });
+    }
+    if (href === `${AUTH}/users/me`) {
+      return Response.json({ user: { id: "user-123" } });
+    }
     throw new Error(`Unexpected upstream call: ${href}`);
   });
 
@@ -106,6 +119,19 @@ const preAuthCookie = () =>
     { algorithm: "HS256", expiresIn: "300s" },
   )}`;
 
+// Each silent refresh needs its own refresh token: core replays a recent
+// refresh result for the same token rather than calling the auth API again.
+let refreshCount = 0;
+const silentRefresh = () => ({
+  method: "get",
+  path: "/users/me",
+  cookie: `seamless-refresh=${jwt.sign(
+    { sub: "user-123", refreshToken: `refresh-${++refreshCount}` },
+    COOKIE_SECRET,
+    { algorithm: "HS256", expiresIn: "3600s" },
+  )}`,
+});
+
 const DOCKER_OPTIONS = { authServerIssuer: DOCKER_ISSUER, audience: DOCKER_ISSUER };
 
 const STEPS = [
@@ -243,6 +269,32 @@ describe("authServerIssuer", () => {
         }
       },
     );
+
+    it("accepts a silent refresh signed by a configured issuer distinct from the URL", async () => {
+      const calls = await mockUpstream(DOCKER_ISSUER);
+
+      const res = await run(silentRefresh(), DOCKER_OPTIONS);
+
+      expect(res.status).toBe(200);
+      expect(res.cookies).toEqual(
+        expect.arrayContaining(["seamless-access", "seamless-refresh"]),
+      );
+      expect(calls.every((href) => href.startsWith(`${AUTH}/`))).toBe(true);
+    });
+
+    it("rejects a silent refresh from an issuer other than the expected one", async () => {
+      await mockUpstream(DOCKER_ISSUER);
+      const unconfigured = await run(silentRefresh(), {});
+
+      await mockUpstream(AUTH);
+      const misconfigured = await run(silentRefresh(), DOCKER_OPTIONS);
+
+      // The 401 clears the session cookies, so their names still appear.
+      for (const res of [unconfigured, misconfigured]) {
+        expect(res.status).toBe(401);
+        expect(res.body).toEqual({ error: "Refresh failed" });
+      }
+    });
   });
 
   it("sets the same session cookies from both adapters with a configured issuer", async () => {
diff --git a/packages/nextjs/src/handler.ts b/packages/nextjs/src/handler.ts
index f72c1ed..37b14ae 100644
--- a/packages/nextjs/src/handler.ts
+++ b/packages/nextjs/src/handler.ts
@@ -231,6 +231,7 @@ async function dispatch(
         issuer: SERVICE_TOKEN_ISSUER,
         audience: SERVICE_TOKEN_AUDIENCE,
         accessTokenAudience: opts.audience,
+        authServerIssuer: opts.authServerIssuer,
         keyId: opts.jwksKid,
         forwardedClientIp: forwardedClientIp(request, opts.resolveClientIp),
         forwardedUserAgent: forwardedUserAgent(request),
diff --git a/packages/nextjs/tests/issuer.parity.test.js b/packages/nextjs/tests/issuer.parity.test.js
index 99e2922..aa22353 100644
--- a/packages/nextjs/tests/issuer.parity.test.js
+++ b/packages/nextjs/tests/issuer.parity.test.js
@@ -93,6 +93,19 @@ async function mockUpstream(issuer) {
         refreshTtl: 2592000,
       });
     }
+    if (href === `${AUTH}/refresh`) {
+      return Response.json({
+        sub: "user-123",
+        token: access,
+        refreshToken: "refresh-2",
+        roles: ["athlete"],
+        ttl: 1800,
+        refreshTtl: 2592000,
+      });
+    }
+    if (href === `${AUTH}/users/me`) {
+      return Response.json({ user: { id: "user-123" } });
+    }
     throw new Error(`Unexpected upstream call: ${href}`);
   });
 
@@ -106,6 +119,19 @@ const preAuthCookie = () =>
     { algorithm: "HS256", expiresIn: "300s" },
   )}`;
 
+// Each silent refresh needs its own refresh token: core replays a recent
+// refresh result for the same token rather than calling the auth API again.
+let refreshCount = 0;
+const silentRefresh = () => ({
+  method: "get",
+  path: "/users/me",
+  cookie: `seamless-refresh=${jwt.sign(
+    { sub: "user-123", refreshToken: `refresh-${++refreshCount}` },
+    COOKIE_SECRET,
+    { algorithm: "HS256", expiresIn: "3600s" },
+  )}`,
+});
+
 const DOCKER_OPTIONS = { authServerIssuer: DOCKER_ISSUER, audience: DOCKER_ISSUER };
 
 const STEPS = [
@@ -243,6 +269,32 @@ describe("authServerIssuer", () => {
         }
       },
     );
+
+    it("accepts a silent refresh signed by a configured issuer distinct from the URL", async () => {
+      const calls = await mockUpstream(DOCKER_ISSUER);
+
+      const res = await run(silentRefresh(), DOCKER_OPTIONS);
+
+      expect(res.status).toBe(200);
+      expect(res.cookies).toEqual(
+        expect.arrayContaining(["seamless-access", "seamless-refresh"]),
+      );
+      expect(calls.every((href) => href.startsWith(`${AUTH}/`))).toBe(true);
+    });
+
+    it("rejects a silent refresh from an issuer other than the expected one", async () => {
+      await mockUpstream(DOCKER_ISSUER);
+      const unconfigured = await run(silentRefresh(), {});
+
+      await mockUpstream(AUTH);
+      const misconfigured = await run(silentRefresh(), DOCKER_OPTIONS);
+
+      // The 401 clears the session cookies, so their names still appear.
+      for (const res of [unconfigured, misconfigured]) {
+        expect(res.status).toBe(401);
+        expect(res.body).toEqual({ error: "Refresh failed" });
+      }
+    });
   });
 
   it("sets the same session cookies from both adapters with a configured issuer", async () => {