diff --git a/cpp/functions/core/http_request.cpp b/cpp/functions/core/http_request.cpp
index bb196165..4f481a03 100644
--- a/cpp/functions/core/http_request.cpp
+++ b/cpp/functions/core/http_request.cpp
@@ -269,8 +269,21 @@ Response request(const Request& req) {
     }
 
     cmd << ' ' << sh_q(req.url)
-        << " -o " << sh_q(tmp_body_out)
-        << " 2>&1";
+        << " -o " << sh_q(tmp_body_out);
+
+    // On POSIX we go through /bin/sh -c via popen, so `2>&1` is a shell redirect.
+    // On Windows we use CreateProcessW (no shell): `2>&1` would be passed as an
+    // extra positional arg to curl, which treats it as a second URL → "Bad
+    // hostname" (exit 3). stderr is already merged via STARTUPINFOW.hStdError.
+#ifndef _WIN32
+    cmd << " 2>&1";
+#endif
+
+    if (std::getenv("FN_HTTP_DEBUG")) {
+        fprintf(stderr, "[fn_http debug] cmdline: %s\n", cmd.str().c_str());
+        fprintf(stderr, "[fn_http debug] req.url=[%s] len=%zu\n",
+                req.url.c_str(), req.url.size());
+    }
 
     // Capture stderr (curl prints transport errors to stderr with -sS).
     std::string curl_stderr;