diff --git a/packages/evals/run.ts b/packages/evals/run.ts
index a524ee4b9e..73926ae8c2 100644
--- a/packages/evals/run.ts
+++ b/packages/evals/run.ts
@@ -13,6 +13,7 @@ if (!wantsHelp && !wantsMan) {
   const build = spawnSync("pnpm", ["run", "build"], {
     stdio: "inherit",
     cwd: "../..",
+    shell: process.platform === "win32",
   });
   if (build.status !== 0) process.exit(build.status ?? 1);
 }
diff --git a/packages/evals/scripts/build-cli.ts b/packages/evals/scripts/build-cli.ts
index 1650fd43e5..553ab44532 100644
--- a/packages/evals/scripts/build-cli.ts
+++ b/packages/evals/scripts/build-cli.ts
@@ -12,8 +12,18 @@ import { getRepoRootDir } from "../runtimePaths.js";
 
 const repoRoot = getRepoRootDir();
 
+import esbuild from "esbuild";
+
 const run = (args: string[]) => {
-  const result = spawnSync("pnpm", args, { stdio: "inherit", cwd: repoRoot });
+  const cmd = process.platform === "win32" ? "pnpm.cmd" : "pnpm";
+  const result = spawnSync(cmd, args, {
+    stdio: "inherit",
+    cwd: repoRoot,
+  });
+  if (result.error) {
+    console.error("Spawn error:", result.error);
+    process.exit(1);
+  }
   if (result.status !== 0) {
     process.exit(result.status ?? 1);
   }
@@ -21,19 +31,18 @@ const run = (args: string[]) => {
 
 fs.mkdirSync(`${repoRoot}/packages/evals/dist/cli`, { recursive: true });
 
-run([
-  "exec",
-  "esbuild",
-  "packages/evals/cli.ts",
-  "--bundle",
-  "--platform=node",
-  "--format=esm",
-  `--outfile=${repoRoot}/packages/evals/dist/cli/cli.js`,
-  "--sourcemap",
-  "--packages=external",
-  "--banner:js=#!/usr/bin/env node",
-  "--log-level=warning",
-]);
+esbuild.buildSync({
+  entryPoints: [`${repoRoot}/packages/evals/cli.ts`],
+  bundle: true,
+  platform: "node",
+  format: "esm",
+  outfile: `${repoRoot}/packages/evals/dist/cli/cli.js`,
+  sourcemap: true,
+  packages: "external",
+  banner: { js: "#!/usr/bin/env node" },
+  logLevel: "warning",
+  absWorkingDir: repoRoot,
+});
 
 /* ── merge config: always update tasks/benchmarks from source, but preserve user defaults ── */
 const sourceConfig = JSON.parse(
@@ -66,6 +75,7 @@ fs.chmodSync(`${repoRoot}/packages/evals/dist/cli/cli.js`, 0o755);
 const link = spawnSync("npm", ["link", "--force"], {
   stdio: "inherit",
   cwd: `${repoRoot}/packages/evals`,
+  shell: process.platform === "win32",
 });
 if (link.status !== 0) {
   console.warn(
diff --git a/packages/evals/scripts/build-esm.ts b/packages/evals/scripts/build-esm.ts
index 4100f6b34e..a8a98a6530 100644
--- a/packages/evals/scripts/build-esm.ts
+++ b/packages/evals/scripts/build-esm.ts
@@ -13,7 +13,15 @@ import { getRepoRootDir } from "../runtimePaths.js";
 const repoRoot = getRepoRootDir();
 
 const run = (args: string[]) => {
-  const result = spawnSync("pnpm", args, { stdio: "inherit", cwd: repoRoot });
+  const result = spawnSync("pnpm", args, {
+    stdio: "inherit",
+    cwd: repoRoot,
+    shell: process.platform === "win32",
+  });
+  if (result.error) {
+    console.error("Spawn error:", result.error);
+    process.exit(1);
+  }
   if (result.status !== 0) {
     process.exit(result.status ?? 1);
   }