diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 961ca2a..a9583a8 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -11,18 +11,21 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
 
     steps:
-    - name: checkout
-      uses: actions/checkout@v1
-      with:
-        fetch-depth: 1
+      - name: checkout
+        uses: actions/checkout@v1
+        with:
+          fetch-depth: 1
 
-    - name: node
-      uses: actions/setup-node@v1
-      with:
-        node-version: ${{ matrix.node-version }}
+      - name: node
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
 
-    - name: install
-      run: yarn
+      - name: install
+        run: yarn
 
-    - name: test
-      run: yarn test
+      - name: test
+        run: yarn test
+
+      - name: test-cjs
+        run: yarn test-cjs
diff --git a/ava.config.js b/ava.config.js
index bd59f81..61cf66b 100644
--- a/ava.config.js
+++ b/ava.config.js
@@ -1,7 +1,7 @@
 export default {
 	files: ['test/*.ts'],
 	extensions: ['ts'],
-	require: ['ts-node/register'],
+	require: ['./email.test.ts'],
 	environmentVariables: {
 		NODE_TLS_REJECT_UNAUTHORIZED: '0',
 	},
diff --git a/email.test.ts b/email.test.ts
new file mode 100644
index 0000000..598d59e
--- /dev/null
+++ b/email.test.ts
@@ -0,0 +1,7 @@
+require('ts-node/register');
+if (process.title === 'cjs') {
+	require('./rollup/email.cjs');
+	require.cache[require.resolve('./email.ts')] =
+		require.cache[require.resolve('./rollup/email.cjs')];
+	console.log('Testing email.cjs...\n');
+}
diff --git a/package.json b/package.json
index 7b803b9..fe6ebfc 100644
--- a/package.json
+++ b/package.json
@@ -56,7 +56,8 @@
 	"scripts": {
 		"build": "rollup -c rollup.config.ts",
 		"lint": "eslint *.ts \"+(smtp|test)/*.ts\"",
-		"test": "ava --serial"
+		"test": "ava --serial",
+		"test-cjs": "npm run build && npm run test -- --node-arguments='--title=cjs'"
 	},
 	"license": "MIT"
 }