diff --git a/packages/bun-release/scripts/upload-npm.ts b/packages/bun-release/scripts/upload-npm.ts
index 353673ebed..dfb76fe39f 100644
--- a/packages/bun-release/scripts/upload-npm.ts
+++ b/packages/bun-release/scripts/upload-npm.ts
@@ -73,9 +73,11 @@ async function buildRootModule(dryRun?: boolean) {
   });
   // Create placeholder scripts that print an error message if postinstall hasn't run.
   // On Unix, these are executed as shell scripts despite the .exe extension.
-  // On Windows, npm creates .cmd wrappers that would fail anyway if the binary isn't valid.
-  const placeholderScript = `#!/bin/sh
-echo "Error: Bun's postinstall script was not run." >&2
+  // Do NOT add a shebang (#!/bin/sh) here — npm's cmd-shim reads shebangs to generate
+  // .ps1/.cmd wrappers BEFORE postinstall runs, and bakes the interpreter path in.
+  // A #!/bin/sh shebang breaks Windows because the wrappers reference /bin/sh which
+  // doesn't exist, even after postinstall replaces the placeholder with the real binary.
+  const placeholderScript = `echo "Error: Bun's postinstall script was not run." >&2
 echo "" >&2
 echo "This occurs when using --ignore-scripts during installation, or when using a" >&2
 echo "package manager like pnpm that does not run postinstall scripts by default." >&2
diff --git a/test/regression/issue/24329.test.ts b/test/regression/issue/24329.test.ts
index f63e1c709a..1c88174ff1 100644
--- a/test/regression/issue/24329.test.ts
+++ b/test/regression/issue/24329.test.ts
@@ -13,8 +13,9 @@ test("bun npm placeholder script should exit with error if postinstall hasn't ru
 
   // This is the placeholder script content that gets written to bin/bun.exe
   // during npm package build (see packages/bun-release/scripts/upload-npm.ts)
-  const placeholderScript = `#!/bin/sh
-echo "Error: Bun's postinstall script was not run." >&2
+  // Note: no shebang — a #!/bin/sh shebang breaks Windows because npm's cmd-shim
+  // bakes the interpreter path into .ps1/.cmd wrappers before postinstall runs.
+  const placeholderScript = `echo "Error: Bun's postinstall script was not run." >&2
 echo "" >&2
 echo "This occurs when using --ignore-scripts during installation, or when using a" >&2
 echo "package manager like pnpm that does not run postinstall scripts by default." >&2
@@ -38,9 +39,11 @@ exit 1
   });
   expect(chmodExitCode).toBe(0);
 
-  // Run the placeholder script
+  // Run via sh explicitly — in real usage, bash/zsh automatically fall back to sh
+  // interpretation when execve returns ENOEXEC for a shebang-less executable file.
+  // Bun.spawn doesn't have that fallback, so we invoke sh directly here.
   await using proc = Bun.spawn({
-    cmd: ["./bun-placeholder", "--version"],
+    cmd: ["sh", "./bun-placeholder"],
     cwd: String(dir),
     env: bunEnv,
     stdout: "pipe",