diff --git a/build.cjs b/build.cjs
deleted file mode 100755
index cbf7259..0000000
--- a/build.cjs
+++ /dev/null
@@ -1,22 +0,0 @@
-#!/usr/bin/env node
-
-const fs = require("fs/promises");
-const child_process = require("child_process");
-
-async function main() {
-  const dir = await fs.opendir("src");
-  for await (const dirent of dir) {
-    if (["-pre.ts", "-main.ts", "-post.ts"].some(x => dirent.name.endsWith(x))) {
-      child_process.exec(`tsup-node src/${dirent.name} --out-dir dist --format esm`, (error, stdout, stderr) => {
-        if (error) {
-          console.error(`exec error: ${error}`);
-          return;
-        }
-        console.log(`stdout: ${stdout}`);
-        console.error(`stderr: ${stderr}`);
-      });
-    }
-  }
-}
-
-main().then();
diff --git a/package.json b/package.json
index bcf23d3..4958c76 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,7 @@
     "format:write": "prettier --write **/*.ts",
     "format:check": "prettier --check **/*.ts",
     "lint": "npx eslint . -c eslint.config.mjs",
-    "build": "./build.cjs",
+    "build": "tsup",
     "build:watch": "npm run package -- --watch",
     "test": "NODE_OPTIONS=\"$NODE_OPTIONS --experimental-vm-modules\" jest --detectOpenHandles",
     "all": "npm run format:write && npm run lint && npm run test && npm run build",
diff --git a/tsup.config.ts b/tsup.config.ts
index 5d5657b..6011320 100644
--- a/tsup.config.ts
+++ b/tsup.config.ts
@@ -1,24 +1,31 @@
-import { defineConfig } from 'tsup'
+import { readdirSync } from "fs";
+import { defineConfig } from "tsup";
+
+const entry = readdirSync("src", { withFileTypes: true })
+  .filter((dirent) => dirent.isFile())
+  .map((dirent) => dirent.name)
+  .filter((name) => ["-pre.ts", "-main.ts", "-post.ts"].some((suffix) => name.endsWith(suffix)))
+  .sort()
+  .map((name) => `src/${name}`);
 
 export default defineConfig({
-    noExternal: [
-        /(.*)/
-    ],
-    dts: false,
-    splitting: false,
-    clean: false,
-    skipNodeModulesBundle: true,
-    shims: true,
-    cjsInterop: false,
-    target: "es2022",
-    format: 'esm',
-    outDir: "dist/",
-    banner: {
-        js: `import { createRequire as __createRequire } from 'module'; const require = __createRequire(import.meta.url);`,
-    },
-    outExtension({ format }) {
-        return {
-            js: `.mjs`,
-        }
-    },
-})
\ No newline at end of file
+  entry,
+  noExternal: [/(.*)/],
+  dts: false,
+  splitting: false,
+  clean: false,
+  skipNodeModulesBundle: true,
+  shims: true,
+  cjsInterop: false,
+  target: "es2022",
+  format: ["esm"],
+  outDir: "dist/",
+  banner: {
+    js: `import { createRequire as __createRequire } from 'module'; const require = __createRequire(import.meta.url);`,
+  },
+  outExtension() {
+    return {
+      js: ".mjs",
+    };
+  },
+});