diff --git a/apps/gateway/src/lib/create-http-response-from-mcp-tool-call-response.ts b/apps/gateway/src/lib/create-http-response-from-mcp-tool-call-response.ts
index 522cdca2..2715d254 100644
--- a/apps/gateway/src/lib/create-http-response-from-mcp-tool-call-response.ts
+++ b/apps/gateway/src/lib/create-http-response-from-mcp-tool-call-response.ts
@@ -5,7 +5,7 @@ import type { GatewayHonoContext, McpToolCallResponse } from './types'
 import { cfValidateJsonSchemaObject } from './cf-validate-json-schema-object'
 
 export async function createHttpResponseFromMcpToolCallResponse(
-  ctx: GatewayHonoContext,
+  _ctx: GatewayHonoContext,
   {
     tool,
     deployment,
@@ -21,6 +21,11 @@ export async function createHttpResponseFromMcpToolCallResponse(
     500,
     `Internal logic error for origin adapter type "${deployment.originAdapter.type}"`
   )
+  assert(
+    !toolCallResponse.isError,
+    502,
+    `MCP tool "${tool.name}" returned an error.`
+  )
 
   if (tool.outputSchema) {
     assert(
diff --git a/readme.md b/readme.md
index f8547250..5aff8857 100644
--- a/readme.md
+++ b/readme.md
@@ -35,6 +35,7 @@
   - MCP origin server support
   - add support for custom headers on responses
   - how to handle binary bodies and responses?
+- add requestId to all JSON error responses
 
 ## TODO Post-MVP