diff --git a/typespec/main.tsp b/typespec/main.tsp
index 6e58193..7b68ed1 100644
--- a/typespec/main.tsp
+++ b/typespec/main.tsp
@@ -430,7 +430,7 @@ namespace Service {
             } | {
                 @statusCode _: 400;
                 @body response: InvalidDocumentResponse | Error;
-            };
+            } | ErrorResponse<404>;
 
             enum Validator {
                 AvalonMediaSystemCSVManifest: "avalon",
diff --git a/typespec/tsp-output/@typespec/openapi3/openapi.v1.yaml b/typespec/tsp-output/@typespec/openapi3/openapi.v1.yaml
index ce32c14..0f1a048 100644
--- a/typespec/tsp-output/@typespec/openapi3/openapi.v1.yaml
+++ b/typespec/tsp-output/@typespec/openapi3/openapi.v1.yaml
@@ -981,6 +981,22 @@ paths:
                 anyOf:
                   - $ref: '#/components/schemas/V2Beta.Validate.InvalidDocumentResponse'
                   - $ref: '#/components/schemas/Error'
+        '404':
+          description: The server cannot find the requested resource.
+          content:
+            application/json:
+              schema:
+                type: object
+                required:
+                  - error
+                  - message
+                properties:
+                  error:
+                    type: boolean
+                    default: true
+                  message:
+                    type: string
+                description: ''
       requestBody:
         required: true
         content: