diff --git a/plugins/codex/scripts/lib/process.mjs b/plugins/codex/scripts/lib/process.mjs
index dd8fc3751..ab913b2f4 100644
--- a/plugins/codex/scripts/lib/process.mjs
+++ b/plugins/codex/scripts/lib/process.mjs
@@ -66,7 +66,13 @@ export function terminateProcessTree(pid, options = {}) {
   if (platform === "win32") {
     const result = runCommandImpl("taskkill", ["/PID", String(pid), "/T", "/F"], {
       cwd: options.cwd,
-      env: options.env
+      env: options.env,
+      // runCommand prefers process.env.SHELL on Windows, so under Git Bash this
+      // ran as `bash -c "taskkill /PID ..."` and MSYS path conversion rewrote
+      // the /PID switch into C:/Program Files/Git/PID, failing every kill with
+      // "ERROR: Invalid argument/option". taskkill takes /-switches and an
+      // argument array, so it does not need a shell.
+      shell: false
     });
 
     if (!result.error && result.status === 0) {
diff --git a/tests/process.test.mjs b/tests/process.test.mjs
index 80e0715b0..f59bd56d4 100644
--- a/tests/process.test.mjs
+++ b/tests/process.test.mjs
@@ -7,8 +7,8 @@ test("terminateProcessTree uses taskkill on Windows", () => {
   let captured = null;
   const outcome = terminateProcessTree(1234, {
     platform: "win32",
-    runCommandImpl(command, args) {
-      captured = { command, args };
+    runCommandImpl(command, args, options) {
+      captured = { command, args, shell: options?.shell };
       return {
         command,
         args,
@@ -26,7 +26,10 @@ test("terminateProcessTree uses taskkill on Windows", () => {
 
   assert.deepEqual(captured, {
     command: "taskkill",
-    args: ["/PID", "1234", "/T", "/F"]
+    args: ["/PID", "1234", "/T", "/F"],
+    // Not through a shell: under Git Bash, MSYS path conversion turns the /PID
+    // switch into C:/Program Files/Git/PID and taskkill rejects it.
+    shell: false
   });
   assert.equal(outcome.delivered, true);
   assert.equal(outcome.method, "taskkill");