diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5050973b..eec529ca 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -48,3 +48,29 @@ jobs:
         if: ${{ matrix.coverage }}
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
+  test-legacy:
+    name: Test - ubuntu-latest - Node v8.9, Webpack 4
+    runs-on: ubuntu-latest
+    env:
+      YARN_NODE_LINKER: node-modules
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js 14.x
+        uses: actions/setup-node@v1
+        with:
+          node-version: 14.x
+      - name: Install dependencies
+        run: yarn
+      - name: Install webpack 4
+        run: yarn add -D webpack@4
+      - name: Build babel-loader
+        run: yarn run build
+        env:
+          BABEL_ENV: test
+      - name: Use Node.js 8.9
+        uses: actions/setup-node@v1
+        with:
+          node-version: '8.9'
+      - name: Run tests for webpack version 4
+        run: node scripts/test-legacy
+
diff --git a/.gitignore b/.gitignore
index ed7463b9..47579869 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,4 @@ test/output
 !.yarn/releases
 .pnp.*
 .vscode
+scripts/test-legacy-source/output
diff --git a/package.json b/package.json
index 55852079..456fa3c4 100644
--- a/package.json
+++ b/package.json
@@ -7,7 +7,7 @@
   ],
   "main": "lib/index.js",
   "engines": {
-    "node": ">= 6.9"
+    "node": ">= 8.9"
   },
   "dependencies": {
     "find-cache-dir": "^2.1.0",
diff --git a/scripts/test-legacy-source/input.js b/scripts/test-legacy-source/input.js
new file mode 100644
index 00000000..c9ff7826
--- /dev/null
+++ b/scripts/test-legacy-source/input.js
@@ -0,0 +1 @@
+class App {}
diff --git a/scripts/test-legacy.js b/scripts/test-legacy.js
new file mode 100644
index 00000000..349b4df8
--- /dev/null
+++ b/scripts/test-legacy.js
@@ -0,0 +1,52 @@
+const webpack = require("webpack");
+const path = require("path");
+const fs = require("fs");
+const assert = require("assert");
+
+const babelLoader = path.join(__dirname, "../lib");
+
+const config = {
+  mode: "development",
+  entry: path.join(__dirname, "test-legacy-source/input.js"),
+  output: {
+    path: path.join(__dirname, "test-legacy-source/output"),
+  },
+  module: {
+    rules: [
+      {
+        test: /\.jsx?/,
+        loader: babelLoader,
+        options: {
+          presets: ["@babel/preset-env"],
+        },
+        exclude: /node_modules/,
+      },
+    ],
+  },
+};
+
+webpack(config, (err, stats) => {
+  assert.strictEqual(err, null);
+  assert.deepStrictEqual(stats.compilation.errors, []);
+  assert.deepStrictEqual(stats.compilation.warnings, []);
+
+  fs.readdir(path.join(__dirname, "test-legacy-source/output"), (err, files) => {
+    assert.strictEqual(err, null);
+    assert.strictEqual(files.length, 1);
+    fs.readFile(path.join(__dirname, "test-legacy-source/output", files[0]), (err, data) => {
+      assert.strictEqual(err, null);
+      const test = "var App = function App()";
+      const subject = data.toString();
+
+      assert.notStrictEqual(subject.indexOf(test), -1);
+
+      console.log("DONE");
+      clearTimeout(timeout);
+    });
+  });
+});
+
+const timeout = setTimeout(() => {
+  console.error("TIMEOUT");
+  process.exit(1);
+}, 10 * 1000);