diff --git a/src/backend/core/services/converter_services.py b/src/backend/core/services/converter_services.py
index ee542b1c7..ce527dcb7 100644
--- a/src/backend/core/services/converter_services.py
+++ b/src/backend/core/services/converter_services.py
@@ -13,6 +13,11 @@ from core.services.jwt_services import JWTService
 
 logger = logging.getLogger(__name__)
 
+# Audience of the admin token y-provider expects. Scoping the token to it
+# prevents an admin JWT issued for another backend service from being
+# replayed against y-provider.
+Y_CONVERTER_AUDIENCE = "y-converter"
+
 
 class ConversionError(Exception):
     """Base exception for conversion-related errors."""
@@ -110,7 +115,8 @@ class YdocConverter:
     @property
     def auth_header(self):
         """Build microservice authentication header."""
-        return f"Bearer {JWTService().get_admin_token()}"
+        token = JWTService().get_admin_token({"aud": Y_CONVERTER_AUDIENCE})
+        return f"Bearer {token}"
 
     def _request(self, url, data, content_type, accept):
         """Make a request to the Y-Provider API."""
diff --git a/src/backend/core/tests/test_services_converter_services.py b/src/backend/core/tests/test_services_converter_services.py
index 345e4fb24..0b6f5183b 100644
--- a/src/backend/core/tests/test_services_converter_services.py
+++ b/src/backend/core/tests/test_services_converter_services.py
@@ -27,14 +27,17 @@ def jwt_settings(settings):
 
 
 def test_auth_header():
-    """The auth header carries an admin JWT signed with the configured key."""
+    """The auth header carries an admin JWT scoped to the y-converter audience."""
     converter = YdocConverter()
 
     scheme, token = converter.auth_header.split(" ")
 
     assert scheme == "Bearer"
-    payload = jwt.decode(token, PUBLIC_KEY, algorithms=["RS256"])
+    payload = jwt.decode(
+        token, PUBLIC_KEY, algorithms=["RS256"], audience="y-converter"
+    )
     assert payload["admin"] is True
+    assert payload["aud"] == "y-converter"
 
 
 def test_convert_empty_text():
diff --git a/src/frontend/servers/y-provider/__tests__/middlewares.test.ts b/src/frontend/servers/y-provider/__tests__/middlewares.test.ts
index cc782f9fa..935abb73c 100644
--- a/src/frontend/servers/y-provider/__tests__/middlewares.test.ts
+++ b/src/frontend/servers/y-provider/__tests__/middlewares.test.ts
@@ -18,6 +18,7 @@ import { httpSecurity } from '@/middlewares';
 import {
   mockJwksEndpoint,
   signAdminToken,
+  signAdminTokenForAudience,
   signAdminTokenWithWrongKey,
   signExpiredAdminToken,
   signToken,
@@ -88,6 +89,19 @@ describe('httpSecurity', () => {
     });
   });
 
+  it('rejects a valid admin JWT issued for another audience', async () => {
+    const token = await signAdminTokenForAudience('some-other-service');
+
+    const response = await request(buildApp())
+      .get('/protected')
+      .set('authorization', `Bearer ${token}`);
+
+    expect(response.status).toBe(401);
+    expect(response.body).toStrictEqual({
+      error: 'Unauthorized: Invalid API Key',
+    });
+  });
+
   it('rejects a validly signed JWT missing the admin claim', async () => {
     const token = await signToken({ sub: 'someone' });
 
diff --git a/src/frontend/servers/y-provider/__tests__/testUtils/adminJwt.ts b/src/frontend/servers/y-provider/__tests__/testUtils/adminJwt.ts
index 66d522aa6..e5ffe3288 100644
--- a/src/frontend/servers/y-provider/__tests__/testUtils/adminJwt.ts
+++ b/src/frontend/servers/y-provider/__tests__/testUtils/adminJwt.ts
@@ -27,7 +27,12 @@ export const signToken = (claims: Record<string, unknown>) =>
     .setExpirationTime('1h')
     .sign(privateKey);
 
-export const signAdminToken = () => signToken({ admin: true });
+export const signAdminToken = () =>
+  signToken({ admin: true, aud: 'y-converter' });
+
+/** An admin token correctly signed but scoped to another service's audience. */
+export const signAdminTokenForAudience = (aud: string) =>
+  signToken({ admin: true, aud });
 
 /** An admin token signed correctly but already past its expiry. */
 export const signExpiredAdminToken = () =>
diff --git a/src/frontend/servers/y-provider/src/middlewares.ts b/src/frontend/servers/y-provider/src/middlewares.ts
index c7364ddac..863afa3b4 100644
--- a/src/frontend/servers/y-provider/src/middlewares.ts
+++ b/src/frontend/servers/y-provider/src/middlewares.ts
@@ -16,14 +16,21 @@ export const corsMiddleware = cors({
 // keeps them until their "kid" no longer matches a token, per jose's own policy.
 const jwks = createRemoteJWKSet(new URL(JWKS_URL));
 
+// Requiring this audience stops a valid admin JWT issued for another service
+// from being replayed against y-provider.
+const Y_CONVERTER_AUDIENCE = 'y-converter';
 export const JWT_ALGORITHM = 'RS256';
 
 /**
- * Verify that the given token is an admin JWT signed by the Django backend.
+ * Verify that the given token is an admin JWT signed by the Django backend
+ * for the y-converter audience.
  */
 const isValidAdminToken = async (token: string): Promise<boolean> => {
   try {
-    const { payload } = await jwtVerify(token, jwks, { algorithms: [JWT_ALGORITHM] });
+    const { payload } = await jwtVerify(token, jwks, {
+      algorithms: [JWT_ALGORITHM],
+      audience: Y_CONVERTER_AUDIENCE,
+    });
     return payload.admin === true;
   } catch {
     return false;