diff --git a/README.md b/README.md
index 1f790fe..670617c 100644
--- a/README.md
+++ b/README.md
@@ -116,3 +116,9 @@ Keycloak의 dedicated audience mapper는 `spa-public` access token에
 아니라 이 `aud`도 검사합니다. `verify-pattern1.sh`는 같은 정상 토큰을
 `deliberately-wrong-audience`를 기대하는 진단 인스턴스에도 제출해 `401`을
 확인합니다.
+
+Keycloak은 `KC_HOSTNAME=http://localhost:8080`을 기준으로 token의 `iss`를
+발급합니다. 정상 Resource Server는 이 외부 issuer 문자열을 검증하되 JWKS는
+Docker 내부의 `http://keycloak:8080`에서 가져옵니다. 진단 인스턴스는 일부러
+`http://wrong-issuer.invalid`를 기대하도록 구성되어, 서명과 audience가
+정상이더라도 issuer mismatch로 `401`을 반환합니다.
diff --git a/docker-compose.yml b/docker-compose.yml
index ee74fcf..0262b60 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -112,6 +112,32 @@ services:
     networks:
       - keycloak-net
 
+  app-wrong-issuer:
+    profiles:
+      - diagnostics
+    build:
+      context: ./backend
+    environment:
+      SERVER_PORT: "8081"
+      SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_ISSUER_URI: http://wrong-issuer.invalid/realms/keycloak-patterns
+      SPRING_SECURITY_OAUTH2_RESOURCESERVER_JWT_JWK_SET_URI: http://keycloak:8080/realms/keycloak-patterns/protocol/openid-connect/certs
+      SECURITY_EXPECTED_AUDIENCE: keycloak-pattern-api
+    ports:
+      - "127.0.0.1:18082:8081"
+    depends_on:
+      keycloak:
+        condition: service_healthy
+    healthcheck:
+      test:
+        - CMD-SHELL
+        - wget -q -O - http://127.0.0.1:8081/actuator/health | grep -q '"status":"UP"'
+      interval: 10s
+      timeout: 5s
+      retries: 12
+      start_period: 20s
+    networks:
+      - keycloak-net
+
   nginx:
     build:
       context: ./frontend
diff --git a/e2e/pattern1.mjs b/e2e/pattern1.mjs
index bfdb312..ea20a31 100644
--- a/e2e/pattern1.mjs
+++ b/e2e/pattern1.mjs
@@ -74,6 +74,17 @@ try {
     );
   }
 
+  if (process.env.WRONG_ISSUER_URL) {
+    const response = await fetch(process.env.WRONG_ISSUER_URL, {
+      headers: { Authorization: `Bearer ${accessToken}` },
+    });
+    assert.equal(
+      response.status,
+      401,
+      "the same signed token must fail when the Resource Server expects another issuer",
+    );
+  }
+
   await page.reload();
   await page.locator('[data-authenticated="false"]').waitFor();
   assert.equal(
@@ -83,7 +94,7 @@ try {
   );
 
   console.log(
-    "pattern1 browser verified: code+PKCE S256, audience positive 200/negative 401, Web Storage token 0, reload clears token",
+    "pattern1 browser verified: code+PKCE S256, audience/issuer negatives 401, Web Storage token 0, reload clears token",
   );
 } finally {
   await browser.close();
diff --git a/scripts/verify-pattern1.sh b/scripts/verify-pattern1.sh
index 9cfa026..e806543 100755
--- a/scripts/verify-pattern1.sh
+++ b/scripts/verify-pattern1.sh
@@ -12,12 +12,15 @@ set +a
 
 docker compose down --volumes --remove-orphans
 docker compose up --build -d --wait
-docker compose --profile diagnostics up -d --wait app-wrong-audience
+docker compose --profile diagnostics up -d --wait \
+  app-wrong-audience \
+  app-wrong-issuer
 
 npm --prefix e2e ci
 E2E_USERNAME=regular-user \
 E2E_PASSWORD="$REGULAR_USER_PASSWORD" \
 WRONG_AUDIENCE_URL=http://localhost:18081/api/me \
+WRONG_ISSUER_URL=http://localhost:18082/api/me \
   npm --prefix e2e run test:pattern1
 
 echo "AP1 verified end to end"