diff --git a/package.json b/package.json
index 2d53be9..a46c43a 100644
--- a/package.json
+++ b/package.json
@@ -22,6 +22,7 @@
     "dist/",
     "completions/",
     "docs/",
+    "scripts/postinstall.js",
     "README.md",
     "LICENSE"
   ],
@@ -45,7 +46,7 @@
   "scripts": {
     "build": "tsc -p tsconfig.build.json",
     "prepublishOnly": "npm run build",
-    "postinstall": "chmod +x node_modules/node-pty/prebuilds/*/spawn-helper 2>/dev/null || true",
+    "postinstall": "node scripts/postinstall.js",
     "prepare": "git config core.hooksPath githooks 2>/dev/null || true; sh scripts/update-nix-hash.sh 2>/dev/null || true",
     "install-completions": "sh scripts/install-completions.sh",
     "typecheck": "tsc",
diff --git a/scripts/postinstall.js b/scripts/postinstall.js
new file mode 100644
index 0000000..6057971
--- /dev/null
+++ b/scripts/postinstall.js
@@ -0,0 +1,46 @@
+// Ensure node-pty's prebuilt `spawn-helper` is executable. Necessary because
+// node-pty's published tarball ships the file with mode 0644 and its own
+// post-install never chmods it. The previous workaround used a relative path
+// (`node_modules/node-pty/prebuilds/*/spawn-helper`) which silently no-ops
+// under pnpm with `enableGlobalVirtualStore`, where node-pty lives in a
+// sibling content-addressed link rather than nested under @myobie/pty.
+//
+// The root-cause fix belongs in microsoft/node-pty; once that ships, this
+// script can be removed entirely.
+
+import * as fs from "node:fs";
+import * as path from "node:path";
+import { createRequire } from "node:module";
+import { pathToFileURL } from "node:url";
+
+if (process.platform === "win32") process.exit(0);
+
+// Resolve from this package's root (package.json sibling), not from the
+// script file, so that node-pty is discoverable regardless of whether
+// node_modules is nested (npm/yarn/bun) or a sibling link (pnpm GVS).
+const pkgDir = path.dirname(new URL(import.meta.url).pathname);
+const requireFromPkg = createRequire(
+  pathToFileURL(path.join(pkgDir, "..", "package.json")),
+);
+
+let nodePtyDir;
+try {
+  nodePtyDir = path.dirname(requireFromPkg.resolve("node-pty/package.json"));
+} catch {
+  console.warn("[@myobie/pty] node-pty not found; skipping spawn-helper chmod");
+  process.exit(0);
+}
+
+const helper = path.join(
+  nodePtyDir,
+  "prebuilds",
+  `${process.platform}-${process.arch}`,
+  "spawn-helper",
+);
+
+try {
+  fs.chmodSync(helper, 0o755);
+} catch {
+  // Acceptable when there's no prebuild for this arch and node-pty was
+  // built from source — node-gyp produces the binary executable already.
+}