diff --git a/integrations/mcp/server.mjs b/integrations/mcp/server.mjs
index 5aa696fa..50b4c9bb 100644
--- a/integrations/mcp/server.mjs
+++ b/integrations/mcp/server.mjs
@@ -112,6 +112,10 @@ function runMixEvalJson(jsonBody) {
       cwd: repoRoot,
       stdio: ["pipe", "pipe", "pipe"],
       env: { ...process.env },
+      // Windows distributes Mix through a command shim, which CreateProcess
+      // cannot launch directly. The command and argument are fixed here.
+      shell: process.platform === "win32",
+      windowsHide: true,
     });
     let out = "";
     let err = "";
diff --git a/integrations/mcp/smoke.mjs b/integrations/mcp/smoke.mjs
index cdce65ed..bd1ec8b0 100755
--- a/integrations/mcp/smoke.mjs
+++ b/integrations/mcp/smoke.mjs
@@ -46,6 +46,14 @@ echo '{"ok":true,"outcome":"ALLOW","status":"accepted","stop_reason":null}'
   const stubPath = path.join(dir, "mix");
   writeFileSync(stubPath, stub);
   chmodSync(stubPath, 0o755);
+
+  // Windows resolves command names through PATHEXT. Keep the smoke stub in
+  // that executable form as well, so the server's normal `spawn("mix", ...)`
+  // path is exercised on both platforms.
+  writeFileSync(
+    path.join(dir, "mix.cmd"),
+    "@echo off\r\nmore > nul\r\necho {\"ok\":true,\"outcome\":\"ALLOW\",\"status\":\"accepted\",\"stop_reason\":null}\r\n",
+  );
   return dir;
 }
 
@@ -100,7 +108,7 @@ function rpcDriver(child) {
 async function main() {
   const stubDir = setupStubMix();
   const child = spawnServer({
-    PATH: `${stubDir}:${process.env.PATH ?? ""}`,
+    PATH: `${stubDir}${path.delimiter}${process.env.PATH ?? ""}`,
     PYTHIA_REPO_ROOT: repoRoot,
   });
   const { call } = rpcDriver(child);