diff --git a/readme.md b/readme.md
index 8459442c..8defdb33 100644
--- a/readme.md
+++ b/readme.md
@@ -40,6 +40,9 @@ $ ncc build input.js -o dist
 
 Outputs the Node.js compact build of `input.js` into `dist/index.js`.
 
+> Note: If the input file is using a `.cjs` extension, then so will the corresponding output file.
+> This is useful for packages that want to use `.js` files as modules in native Node.js using
+> a `"type": "module"` in the package.json file.
 
 #### Commands:
 ```
diff --git a/src/cli.js b/src/cli.js
index f7b20d32..da3f7d55 100755
--- a/src/cli.js
+++ b/src/cli.js
@@ -1,6 +1,6 @@
 #!/usr/bin/env node
 
-const { resolve, relative, dirname, sep } = require("path");
+const { resolve, relative, dirname, sep, extname } = require("path");
 const glob = require("glob");
 const shebangRegEx = require("./utils/shebang");
 const rimraf = require("rimraf");
@@ -50,7 +50,7 @@ else {
   api = true;
 }
 
-function renderSummary(code, map, assets, outDir, buildTime) {
+function renderSummary(code, map, assets, ext, outDir, buildTime) {
   if (outDir && !outDir.endsWith(sep)) outDir += sep;
   const codeSize = Math.round(Buffer.byteLength(code, "utf8") / 1024);
   const mapSize = map ? Math.round(Buffer.byteLength(map, "utf8") / 1024) : 0;
@@ -74,10 +74,10 @@ function renderSummary(code, map, assets, outDir, buildTime) {
 
   let indexRender = `${codeSize
     .toString()
-    .padStart(sizePadding, " ")}kB  ${outDir}${"index.js"}`;
+    .padStart(sizePadding, " ")}kB  ${outDir}index${ext}`;
   let indexMapRender = map ? `${mapSize
     .toString()
-    .padStart(sizePadding, " ")}kB  ${outDir}${"index.js.map"}` : '';
+    .padStart(sizePadding, " ")}kB  ${outDir}index${ext}.map` : '';
 
   let output = "",
     first = true;
@@ -215,6 +215,7 @@ async function runCmd (argv, stdout, stderr) {
       let startTime = Date.now();
       let ps;
       const buildFile = eval("require.resolve")(resolve(args._[1] || "."));
+      const ext = buildFile.endsWith('.cjs') ? '.cjs' : '.js';
       const ncc = require("./index.js")(
         buildFile,
         {
@@ -241,16 +242,16 @@ async function runCmd (argv, stdout, stderr) {
 
         outDir = outDir || resolve("dist");
         mkdirp.sync(outDir);
-        // remove all existing ".js" files in the out directory
+        // remove all existing ".js" and ".cjs" files in the out directory
         await Promise.all(
           (await new Promise((resolve, reject) =>
-            glob(outDir + '/**/*.js', (err, files) => err ? reject(err) : resolve(files))
+            glob(outDir + '/**/*.(js|cjs)', (err, files) => err ? reject(err) : resolve(files))
           )).map(file =>
             new Promise((resolve, reject) => unlink(file, err => err ? reject(err) : resolve())
           ))
         );
-        writeFileSync(outDir + "/index.js", code, { mode: code.match(shebangRegEx) ? 0o777 : 0o666 });
-        if (map) writeFileSync(outDir + "/index.js.map", map);
+        writeFileSync(`${outDir}/index${ext}`, code, { mode: code.match(shebangRegEx) ? 0o777 : 0o666 });
+        if (map) writeFileSync(`${outDir}/index${ext}.map`, map);
 
         for (const asset of Object.keys(assets)) {
           const assetPath = outDir + "/" + asset;
@@ -269,6 +270,7 @@ async function runCmd (argv, stdout, stderr) {
               code,
               map,
               assets,
+              ext,
               run ? "" : relative(process.cwd(), outDir),
               Date.now() - startTime,
             ) + '\n'
@@ -292,7 +294,7 @@ async function runCmd (argv, stdout, stderr) {
           } while (nodeModulesDir = resolve(nodeModulesDir, "../../node_modules"));
           if (nodeModulesDir)
             symlinkSync(nodeModulesDir, outDir + "/node_modules", "junction");
-          ps = require("child_process").fork(outDir + "/index.js", {
+          ps = require("child_process").fork(`${outDir}/index${ext}`, {
             stdio: api ? 'pipe' : 'inherit'
           });
           if (api) {
diff --git a/src/index.js b/src/index.js
index fd2e4c37..1e5043f7 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,22 +1,19 @@
 const resolve = require("resolve");
 const fs = require("graceful-fs");
 const crypto = require("crypto");
-const { sep, join, dirname } = require("path");
+const { join, dirname, extname } = require("path");
 const webpack = require("webpack");
 const MemoryFS = require("memory-fs");
 const terser = require("terser");
 const tsconfigPaths = require("tsconfig-paths");
 const TsconfigPathsPlugin = require("tsconfig-paths-webpack-plugin");
 const shebangRegEx = require('./utils/shebang');
-const { pkgNameRegEx } = require("./utils/get-package-base");
 const nccCacheDir = require("./utils/ncc-cache-dir");
 const { version: nccVersion } = require('../package.json');
 
 // support glob graceful-fs
 fs.gracefulify(require("fs"));
 
-const nodeBuiltins = new Set([...require("repl")._builtinLibs, "constants", "module", "timers", "console", "_stream_writable", "_stream_readable", "_stream_duplex"]);
-
 const SUPPORTED_EXTENSIONS = [".js", ".json", ".node", ".mjs", ".ts", ".tsx"];
 
 const hashOf = name => {
@@ -36,7 +33,7 @@ module.exports = (
   {
     cache,
     externals = [],
-    filename = "index.js",
+    filename = 'index' + (entry.endsWith('.cjs') ? '.cjs' : '.js'),
     minify = false,
     sourceMap = false,
     sourceMapRegister = true,
@@ -49,6 +46,8 @@ module.exports = (
     transpileOnly = false
   } = {}
 ) => {
+  const ext = extname(filename);
+
   if (!quiet) {
     console.log(`ncc: Version ${nccVersion}`);
     console.log(`ncc: Compiling file ${filename}`);
@@ -61,11 +60,11 @@ module.exports = (
   const existingAssetNames = [filename];
   if (sourceMap) {
     existingAssetNames.push(`${filename}.map`);
-    existingAssetNames.push('sourcemap-register.js');
+    existingAssetNames.push(`sourcemap-register${ext}`);
   }
   if (v8cache) {
     existingAssetNames.push(`${filename}.cache`);
-    existingAssetNames.push(`${filename}.cache.js`);
+    existingAssetNames.push(`${filename}.cache${ext}`);
   }
   const resolvePlugins = [];
   // add TsconfigPathsPlugin to support `paths` resolution in tsconfig
@@ -140,7 +139,8 @@ module.exports = (
     target: "node",
     output: {
       path: "/",
-      filename,
+      // Webpack only emits sourcemaps for files ending in .js
+      filename: ext === '.cjs' ? filename + '.js' : filename,
       libraryTarget: "commonjs2"
     },
     resolve: {
@@ -341,10 +341,12 @@ module.exports = (
       if (resolved in assets)
         symlinks[key] = value;
     }
-    delete assets[filename];
-    delete assets[`${filename}.map`];
-    let code = mfs.readFileSync(`/${filename}`, "utf8");
-    let map = sourceMap ? mfs.readFileSync(`/${filename}.map`, "utf8") : null;
+    // Webpack only emits sourcemaps for .js files
+    // so we need to adjust the .cjs extension handling
+    delete assets[filename + (ext === '.cjs' ? '.js' : '')];
+    delete assets[`${filename}${ext === '.cjs' ? '.js' : ''}.map`];
+    let code = mfs.readFileSync(`/${filename}${ext === '.cjs' ? '.js' : ''}`, "utf8");
+    let map = sourceMap ? mfs.readFileSync(`/${filename}${ext === '.cjs' ? '.js' : ''}.map`, "utf8") : null;
 
     if (map) {
       map = JSON.parse(map);
@@ -385,15 +387,15 @@ module.exports = (
 
     if (v8cache) {
       const { Script } = require('vm');
-      assets[filename + '.cache'] = { source: new Script(code).createCachedData(), permissions: defaultPermissions };
-      assets[filename + '.cache.js'] = { source: code, permissions: defaultPermissions };
+      assets[`${filename}.cache`] = { source: new Script(code).createCachedData(), permissions: defaultPermissions };
+      assets[`${filename}.cache${ext}`] = { source: code, permissions: defaultPermissions };
       if (map) {
         assets[filename + '.map'] = { source: JSON.stringify(map), permissions: defaultPermissions };
         map = undefined;
       }
       code =
         `const { readFileSync, writeFileSync } = require('fs'), { Script } = require('vm'), { wrap } = require('module');\n` +
-        `const source = readFileSync(__dirname + '/${filename}.cache.js', 'utf-8');\n` +
+        `const source = readFileSync(__dirname + '/${filename}.cache${ext}', 'utf-8');\n` +
         `const cachedData = !process.pkg && require('process').platform !== 'win32' && readFileSync(__dirname + '/${filename}.cache');\n` +
         `const script = new Script(wrap(source), cachedData ? { cachedData } : {});\n` +
         `(script.runInThisContext())(exports, require, module, __filename, __dirname);\n` +
@@ -401,8 +403,8 @@ module.exports = (
     }
 
     if (sourceMap && sourceMapRegister) {
-      code = `require('./sourcemap-register.js');` + code;
-      assets['sourcemap-register.js'] = { source: fs.readFileSync(__dirname + "/sourcemap-register.js.cache.js"), permissions: defaultPermissions };
+      code = `require('./sourcemap-register${ext}');` + code;
+      assets[`sourcemap-register${ext}`] = { source: fs.readFileSync(`${__dirname}/sourcemap-register.js.cache.js`), permissions: defaultPermissions };
     }
 
     if (shebangMatch) {
diff --git a/test/cli.js b/test/cli.js
index 0aeda08e..54e6dda9 100644
--- a/test/cli.js
+++ b/test/cli.js
@@ -51,5 +51,17 @@
   {
     args: ["run", "-t", "test/fixtures/with-type-errors/ts-error.ts"],
     expect: { code: 0 }
+  },
+  {
+    args: ["build", "-o", "tmp", "test/fixtures/test.cjs"],
+    expect (code, stdout, stderr) {
+      return stdout.toString().indexOf('tmp/index.cjs') !== -1;
+    }
+  },
+  {
+    args: ["build", "-o", "tmp", "test/fixtures/test.mjs"],
+    expect (code, stdout, stderr) {
+      return stdout.toString().indexOf('tmp/index.js') !== -1;
+    }
   }
 ]
\ No newline at end of file
diff --git a/test/fixtures/test.cjs b/test/fixtures/test.cjs
new file mode 100644
index 00000000..37a46484
--- /dev/null
+++ b/test/fixtures/test.cjs
@@ -0,0 +1 @@
+module.exports = 'test';
diff --git a/test/fixtures/test.mjs b/test/fixtures/test.mjs
new file mode 100644
index 00000000..37a46484
--- /dev/null
+++ b/test/fixtures/test.mjs
@@ -0,0 +1 @@
+module.exports = 'test';