diff --git a/src/utils/net/headers.ts b/src/utils/net/headers.ts
index a0209cd..a481ff4 100644
--- a/src/utils/net/headers.ts
+++ b/src/utils/net/headers.ts
@@ -270,6 +270,6 @@ export function inferHttpRequestBodyHeaders(body: HttpRequestBody): Headers {
         undefined;
 
     headers["Content-Type"] = type;
-    headers["Content-Length"] = length;
+    headers["Content-Length"] = String(length);
     return headers;
 }