diff --git a/.gitignore b/.gitignore
index d838984..7928a65 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 node_modules/
 npm-debug.*
 umd/index.js
+umd/types.d.ts
diff --git a/package.json b/package.json
index 5e65c85..b09677b 100644
--- a/package.json
+++ b/package.json
@@ -32,7 +32,7 @@
     }
   },
   "scripts": {
-    "build": "esm2umd Long index.js > umd/index.js && prettier --write umd/index.js",
+    "build": "node scripts/build.js",
     "lint": "prettier --check .",
     "format": "prettier --write .",
     "test": "npm run test:unit && npm run test:typescript",
@@ -42,10 +42,11 @@
   "files": [
     "index.js",
     "index.d.ts",
+    "types.d.ts",
     "umd/index.js",
     "umd/index.d.ts",
+    "umd/types.d.ts",
     "umd/package.json",
-    "types.d.ts",
     "LICENSE",
     "README.md"
   ],
diff --git a/scripts/build.js b/scripts/build.js
new file mode 100644
index 0000000..8e5769d
--- /dev/null
+++ b/scripts/build.js
@@ -0,0 +1,26 @@
+import fs from "fs";
+import path from "path";
+import { fileURLToPath } from "url";
+import esm2umd from "esm2umd";
+import prettier from "prettier";
+
+const basePath = path.join(path.dirname(fileURLToPath(import.meta.url)), "..");
+const esmPath = path.join(basePath, "index.js");
+const umdPath = path.join(basePath, "umd", "index.js");
+
+const esmSource = fs.readFileSync(esmPath, "utf8");
+const umdSource = esm2umd("Long", esmSource);
+
+async function formatWithPrettier(source, filepath) {
+  const options = await prettier.resolveConfig(filepath);
+  return await prettier.format(source, { ...options, filepath });
+}
+
+const prettierUmdSource = await formatWithPrettier(umdSource, umdPath);
+
+fs.writeFileSync(umdPath, prettierUmdSource);
+
+fs.copyFileSync(
+  path.join(basePath, "types.d.ts"),
+  path.join(basePath, "umd", "types.d.ts"),
+);
diff --git a/tests/typescript/test-global.ts b/tests/typescript/test-global.ts
index dd3b0a8..838df6b 100644
--- a/tests/typescript/test-global.ts
+++ b/tests/typescript/test-global.ts
@@ -1,5 +1,8 @@
 /// <reference path="../../umd/index.d.ts" />
 
 Long.fromValue(1);
+
 var long = new Long(0, 0);
 long.toNumber();
+
+function test(long: Long) {}
diff --git a/tests/typescript/test-import.ts b/tests/typescript/test-import.ts
index 1e2472a..dc3b440 100644
--- a/tests/typescript/test-import.ts
+++ b/tests/typescript/test-import.ts
@@ -1,7 +1,10 @@
 import Long from "../../index.js";
 
 Long.fromValue(1);
+
 var long = new Long(0, 0);
 long.toNumber();
 
+function test(long: Long) {}
+
 export default Long;
diff --git a/tests/typescript/test-require.ts b/tests/typescript/test-require.ts
index 82c2aeb..af0bd6c 100644
--- a/tests/typescript/test-require.ts
+++ b/tests/typescript/test-require.ts
@@ -1,7 +1,10 @@
 import Long = require("../../umd/index.js");
 
 Long.fromValue(1);
+
 var long = new Long(0, 0);
 long.toNumber();
 
-export default Long;
+function test(long: Long) {}
+
+export = Long;
diff --git a/types.d.ts b/types.d.ts
index c8eaf14..7693ca4 100644
--- a/types.d.ts
+++ b/types.d.ts
@@ -1,3 +1,7 @@
+// Common type definitions for both the ESM and UMD variants. The ESM variant
+// reexports the Long class as its default export, whereas the UMD variant makes
+// the Long class a whole-module export with a global variable fallback.
+
 type LongLike =
   | Long
   | number
diff --git a/umd/index.d.ts b/umd/index.d.ts
index 50f20bc..5036689 100644
--- a/umd/index.d.ts
+++ b/umd/index.d.ts
@@ -1,3 +1,3 @@
-import { Long } from "../types.js";
+import { Long } from "./types.js";
 export = Long;
 export as namespace Long;