diff --git a/src/server/sse.test.ts b/src/server/sse.test.ts
index 38ba9e59..9fb1f30c 100644
--- a/src/server/sse.test.ts
+++ b/src/server/sse.test.ts
@@ -264,7 +264,7 @@ describe('SSEServerTransport', () => {
         await transport.handlePostMessage(mockReq, mockHandleRes, { jsonrpc: '2.0', method: 'test' });
 
         expect(mockHandleRes.writeHead).toHaveBeenCalledWith(400);
-        expect(mockHandleRes.end).toHaveBeenCalledWith('Error: Content-Type must start with application/json, got: text/plain');
+        expect(mockHandleRes.end).toHaveBeenCalledWith('Error: Unsupported content-type: text/plain');
       });
     });
 
diff --git a/src/server/sse.ts b/src/server/sse.ts
index 65e8c7c8..73c74bb3 100644
--- a/src/server/sse.ts
+++ b/src/server/sse.ts
@@ -155,7 +155,7 @@ export class SSEServerTransport implements Transport {
     try {
       const ct = contentType.parse(req.headers["content-type"] ?? "");
       if (ct.type !== "application/json") {
-        throw new Error(`Unsupported content-type: ${ct}`);
+        throw new Error(`Unsupported content-type: ${ct.type}`);
       }
 
       body = parsedBody ?? await getRawBody(req, {