diff --git a/src/index.js b/src/index.js
index 92a6aaa7..bbe672a4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -124,7 +124,7 @@ class MiniCssExtractPlugin {
     this.options = Object.assign(
       {
         filename: DEFAULT_FILENAME,
-        moduleFilename: () => options.filename || DEFAULT_FILENAME,
+        moduleFilename: () => this.options.filename || DEFAULT_FILENAME,
         ignoreOrder: false,
       },
       options
diff --git a/test/cases/moduleFilenameMutableFilename/expected/mutated.css b/test/cases/moduleFilenameMutableFilename/expected/mutated.css
new file mode 100644
index 00000000..b9f60c7d
--- /dev/null
+++ b/test/cases/moduleFilenameMutableFilename/expected/mutated.css
@@ -0,0 +1,4 @@
+body {
+  background: palegreen;
+}
+
diff --git a/test/cases/moduleFilenameMutableFilename/index.js b/test/cases/moduleFilenameMutableFilename/index.js
new file mode 100644
index 00000000..aa3357bf
--- /dev/null
+++ b/test/cases/moduleFilenameMutableFilename/index.js
@@ -0,0 +1 @@
+import './style.css';
diff --git a/test/cases/moduleFilenameMutableFilename/style.css b/test/cases/moduleFilenameMutableFilename/style.css
new file mode 100644
index 00000000..9373d1a0
--- /dev/null
+++ b/test/cases/moduleFilenameMutableFilename/style.css
@@ -0,0 +1,3 @@
+body {
+  background: palegreen;
+}
diff --git a/test/cases/moduleFilenameMutableFilename/webpack.config.js b/test/cases/moduleFilenameMutableFilename/webpack.config.js
new file mode 100644
index 00000000..cf8cfbe2
--- /dev/null
+++ b/test/cases/moduleFilenameMutableFilename/webpack.config.js
@@ -0,0 +1,27 @@
+const Self = require('../../../');
+
+module.exports = {
+  entry: {
+    main: './index.js',
+  },
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [Self.loader, 'css-loader'],
+      },
+    ],
+  },
+  output: {
+    filename: '[name].js',
+  },
+  plugins: [
+    (() => {
+      const self = new Self({ filename: 'constructed.css' });
+
+      self.options.filename = 'mutated.css';
+
+      return self;
+    })(),
+  ],
+};