diff --git a/packages/backend/src/services/oidc.service.ts b/packages/backend/src/services/oidc.service.ts
index 250d3d4..dcc05c7 100644
--- a/packages/backend/src/services/oidc.service.ts
+++ b/packages/backend/src/services/oidc.service.ts
@@ -120,7 +120,10 @@ export async function validateIdToken(idToken: string, nonce: string): Promise<O
     jwksCache = { uri: doc.jwks_uri, set: createRemoteJWKSet(new URL(doc.jwks_uri)) };
   }
   const { payload } = await jwtVerify(idToken, jwksCache.set, {
-    issuer: env.OIDC_ISSUER_URL,
+    // getEnv normalizes the configured URL, but providers such as Authentik
+    // publish a scoped issuer with a trailing slash in the discovery document
+    // and id_token. Accept both equivalent wire representations.
+    issuer: [env.OIDC_ISSUER_URL, `${env.OIDC_ISSUER_URL}/`],
     audience: env.OIDC_CLIENT_ID,
   });
   if (payload.nonce !== nonce) {
diff --git a/packages/backend/src/tests/oidc-service.test.ts b/packages/backend/src/tests/oidc-service.test.ts
index 942689b..ff31e31 100644
--- a/packages/backend/src/tests/oidc-service.test.ts
+++ b/packages/backend/src/tests/oidc-service.test.ts
@@ -28,10 +28,10 @@ let nextIdToken = "";
 let certDir: string | null = null;
 let prevTlsRejectUnauthorized: string | undefined;
 
-async function signIdToken(claims: Record<string, unknown>): Promise<string> {
+async function signIdToken(claims: Record<string, unknown>, tokenIssuer = issuer): Promise<string> {
   return new SignJWT(claims)
     .setProtectedHeader({ alg: "ES256", kid: "test-kid" })
-    .setIssuer(issuer)
+    .setIssuer(tokenIssuer)
     .setAudience(CLIENT_ID)
     .setSubject("sub-123")
     .setExpirationTime("5m")
@@ -241,6 +241,22 @@ describe("token exchange + id_token validation", () => {
     await expect(validateIdToken(idToken, "nonce-1")).rejects.toThrow();
   });
 
+  test("accepts an id_token whose issuer has a trailing slash", async () => {
+    resetOidcServiceForTesting();
+    trailingSlashIssuer = true;
+    try {
+      const idToken = await signIdToken(
+        { email: "alice@example.com", email_verified: true, nonce: "nonce-1" },
+        `${issuer}/`,
+      );
+      const info = await validateIdToken(idToken, "nonce-1");
+      expect(info.email).toBe("alice@example.com");
+    } finally {
+      trailingSlashIssuer = false;
+      resetOidcServiceForTesting();
+    }
+  });
+
   test("id_token with wrong audience is rejected", async () => {
     const idToken = await new SignJWT({ email_verified: true })
       .setProtectedHeader({ alg: "ES256", kid: "test-kid" })