diff --git a/src/server/sse.ts b/src/server/sse.ts
index fe03182..341b4ea 100644
--- a/src/server/sse.ts
+++ b/src/server/sse.ts
@@ -68,7 +68,7 @@ export class SSEServerTransport implements Transport {
   async handlePostMessage(
     req: IncomingMessage,
     res: ServerResponse,
-    parsedBody?: unknown,
+    parsedBody?: {[key: string]: unknown},
   ): Promise<void> {
     if (!this._sseResponse) {
       const message = "SSE connection not established";
@@ -76,7 +76,7 @@ export class SSEServerTransport implements Transport {
       throw new Error(message);
     }
 
-    let body: string | unknown;
+    let body: string | typeof parsedBody;
     try {
       const ct = contentType.parse(req.headers["content-type"] ?? "");
       if (ct.type !== "application/json") {