diff --git a/src/shared/protocol.ts b/src/shared/protocol.ts
index 19ff97d3..07bfc02c 100644
--- a/src/shared/protocol.ts
+++ b/src/shared/protocol.ts
@@ -3,6 +3,7 @@ import {
   CancelledNotificationSchema,
   ClientCapabilities,
   ErrorCode,
+  isJSONRPCError,
   isJSONRPCRequest,
   isJSONRPCResponse,
   isJSONRPCNotification,
@@ -274,7 +275,7 @@ export abstract class Protocol<
     };
 
     this._transport.onmessage = (message) => {
-      if (isJSONRPCResponse(message)) {
+      if (isJSONRPCResponse(message) || isJSONRPCError(message)) {
         this._onresponse(message);
       } else if (isJSONRPCRequest(message)) {
         this._onrequest(message);
diff --git a/src/types.ts b/src/types.ts
index a68c3ff1..db6bf125 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -150,6 +150,9 @@ export const JSONRPCErrorSchema = z
   })
   .strict();
 
+export const isJSONRPCError = (value: unknown): value is JSONRPCError =>
+  JSONRPCErrorSchema.safeParse(value).success;
+
 export const JSONRPCMessageSchema = z.union([
   JSONRPCRequestSchema,
   JSONRPCNotificationSchema,