diff --git a/src/index.js b/src/index.js
index db5c40e..7ddf39e 100644
--- a/src/index.js
+++ b/src/index.js
@@ -66,6 +66,32 @@ const createContext = (ctx) => {
   return ctx
 }
 
+// prefers require, checks for ERR_REQUIRE_ESM, which is still experimental, but often works when called synchronous
+const requireOrImport = filepath => {
+  try {
+    return require(filepath)
+  } catch (error) {
+    // importing ECMAScript modules from CommonJS does not work, so load it using dynamic import(...)
+    if (error.code === 'ERR_REQUIRE_ESM') {
+      return import(filepath).then(mod => mod.default)
+    }
+    throw error
+  }
+}
+
+// prefers import, which won't work in sync mode
+const importOrRequire = async filepath => {
+  try {
+    return (await import(filepath)).default
+  } catch (error) {
+    // Node.js 10 does not support dynamic import(...) and throws 'Error: Not supported'
+    if (error.message === 'Not supported') {
+      return require(filepath)
+    }
+    throw error
+  }
+}
+
 const addTypeScriptLoader = (options = {}, loader) => {
   const moduleName = 'postcss'
 
@@ -81,14 +107,19 @@ const addTypeScriptLoader = (options = {}, loader) => {
       `.${moduleName}rc.ts`,
       `.${moduleName}rc.js`,
       `.${moduleName}rc.cjs`,
+      `.${moduleName}rc.mjs`,
       `${moduleName}.config.ts`,
       `${moduleName}.config.js`,
-      `${moduleName}.config.cjs`
+      `${moduleName}.config.cjs`,
+      `${moduleName}.config.mjs`
     ],
     loaders: {
       ...options.loaders,
       '.yaml': (filepath, content) => yaml.parse(content),
       '.yml': (filepath, content) => yaml.parse(content),
+      '.js': requireOrImport,
+      '.cjs': requireOrImport,
+      '.mjs': requireOrImport,
       '.ts': loader
     }
   }
diff --git a/test/js.test.js b/test/js.test.js
index e5bb6b7..9fbef83 100644
--- a/test/js.test.js
+++ b/test/js.test.js
@@ -70,7 +70,7 @@ test('postcss.config.js - {Object} - Process SSS', () => {
   })
 })
 
-describe('postcss.config.js - {Array} - Load Config', () => {
+describe('postcss.config.js (CommonJS) - {Array} - Load Config', () => {
   const ctx = {
     parser: true,
     syntax: true
@@ -88,27 +88,59 @@ describe('postcss.config.js - {Array} - Load Config', () => {
     expect(typeof config.plugins[1]).toBe('object')
 
     expect(config.file)
-      .toEqual(path.resolve('test/js/array', 'postcss.config.js'))
+      .toEqual(path.resolve('test/js/array/cjs-in-js', 'postcss.config.js'))
   }
 
   test('Async', () => {
-    return postcssrc(ctx, 'test/js/array').then(expected)
+    return postcssrc(ctx, 'test/js/array/cjs-in-js').then(expected)
   })
 
   test('Sync', () => {
-    const config = postcssrc.sync(ctx, 'test/js/array')
+    const config = postcssrc.sync(ctx, 'test/js/array/cjs-in-js')
 
     expected(config)
   })
 })
 
-test('postcss.config.js - {Array} - Process CSS', () => {
+describe('postcss.config.cjs - {Array} - Load Config', () => {
+    const ctx = {
+        parser: true,
+        syntax: true
+    }
+
+    const expected = (config) => {
+        expect(config.options.parser).toEqual(require('sugarss'))
+        expect(config.options.syntax).toEqual(require('sugarss'))
+        expect(config.options.map).toEqual(false)
+        expect(config.options.from).toEqual('./test/js/array/fixtures/index.css')
+        expect(config.options.to).toEqual('./test/js/array/expect/index.css')
+
+        expect(config.plugins.length).toEqual(2)
+        expect(typeof config.plugins[0]).toBe('object')
+        expect(typeof config.plugins[1]).toBe('object')
+
+        expect(config.file)
+            .toEqual(path.resolve('test/js/array/cjs', 'postcss.config.cjs'))
+    }
+
+    test('Async', () => {
+        return postcssrc(ctx, 'test/js/array/cjs').then(expected)
+    })
+
+    test('Sync', () => {
+        const config = postcssrc.sync(ctx, 'test/js/array/cjs')
+
+        expected(config)
+    })
+})
+
+test('postcss.config.js (CommonJS) - {Array} - Process CSS', () => {
   const ctx = {
     parser: false,
     syntax: false
   }
 
-  return postcssrc(ctx, 'test/js/array').then((config) => {
+  return postcssrc(ctx, 'test/js/array/cjs').then((config) => {
     return postcss(config.plugins)
       .process(fixture('js/array', 'index.css'), config.options)
       .then((result) => {
@@ -117,14 +149,14 @@ test('postcss.config.js - {Array} - Process CSS', () => {
   })
 })
 
-test('postcss.config.js - {Array} - Process SSS', () => {
+test('postcss.config.js (CommonJS) - {Array} - Process SSS', () => {
   const ctx = {
     from: './test/js/array/fixtures/index.sss',
     parser: true,
     syntax: false
   }
 
-  return postcssrc(ctx, 'test/js/array').then((config) => {
+  return postcssrc(ctx, 'test/js/array/cjs').then((config) => {
     return postcss(config.plugins)
       .process(fixture('js/array', 'index.sss'), config.options)
       .then((result) => {
@@ -132,3 +164,35 @@ test('postcss.config.js - {Array} - Process SSS', () => {
       })
   })
 })
+
+describe('postcss.config.mjs - {Array} - Load Config', () => {
+    const ctx = {
+        parser: true,
+        syntax: true
+    }
+
+    const expected = (config) => {
+        expect(config.options.parser).toEqual(require('sugarss'))
+        expect(config.options.syntax).toEqual(require('sugarss'))
+        expect(config.options.map).toEqual(false)
+        expect(config.options.from).toEqual('./test/js/array/fixtures/index.css')
+        expect(config.options.to).toEqual('./test/js/array/expect/index.css')
+
+        expect(config.plugins.length).toEqual(2)
+        expect(typeof config.plugins[0]).toBe('object')
+        expect(typeof config.plugins[1]).toBe('object')
+
+        expect(config.file)
+            .toEqual(path.resolve('test/js/array/mjs', 'postcss.config.mjs'))
+    }
+
+    test('Async', () => {
+        return postcssrc(ctx, 'test/js/array/mjs').then(expected)
+    })
+
+    xtest('Sync', () => {
+        const config = postcssrc.sync(ctx, 'test/js/array/mjs')
+
+        expected(config)
+    })
+})
diff --git a/test/js/array/postcss.config.js b/test/js/array/cjs-in-js/postcss.config.js
similarity index 100%
rename from test/js/array/postcss.config.js
rename to test/js/array/cjs-in-js/postcss.config.js
diff --git a/test/js/array/cjs/postcss.config.cjs b/test/js/array/cjs/postcss.config.cjs
new file mode 100644
index 0000000..dd76557
--- /dev/null
+++ b/test/js/array/cjs/postcss.config.cjs
@@ -0,0 +1,14 @@
+module.exports = function (ctx) {
+  return {
+    parser: ctx.parser ? 'sugarss' : false,
+    syntax: ctx.syntax ? 'sugarss' : false,
+    map: ctx.map ? 'inline' : false,
+    from: './test/js/array/fixtures/index.css',
+    to: './test/js/array/expect/index.css',
+    plugins: [
+      require('postcss-import')(),
+      require('postcss-nested')(),
+      ctx.env === 'production' ? require('cssnano')() : false
+    ]
+  }
+}
diff --git a/test/js/array/esm-in-js/package.json b/test/js/array/esm-in-js/package.json
new file mode 100644
index 0000000..6990891
--- /dev/null
+++ b/test/js/array/esm-in-js/package.json
@@ -0,0 +1 @@
+{"type": "module"}
diff --git a/test/js/array/esm-in-js/postcss.config.js b/test/js/array/esm-in-js/postcss.config.js
new file mode 100644
index 0000000..47194ce
--- /dev/null
+++ b/test/js/array/esm-in-js/postcss.config.js
@@ -0,0 +1,18 @@
+import postcssImport from 'postcss-import'
+import postcssNested from 'postcss-nested'
+import cssnano from 'cssnano'
+
+export default function (ctx) {
+  return {
+    parser: ctx.parser ? 'sugarss' : false,
+    syntax: ctx.syntax ? 'sugarss' : false,
+    map: ctx.map ? 'inline' : false,
+    from: './test/js/array/fixtures/index.css',
+    to: './test/js/array/expect/index.css',
+    plugins: [
+      postcssImport(),
+      postcssNested(),
+      ctx.env === 'production' ? cssnano() : false
+    ]
+  }
+}
diff --git a/test/js/array/mjs/postcss.config.mjs b/test/js/array/mjs/postcss.config.mjs
new file mode 100644
index 0000000..47194ce
--- /dev/null
+++ b/test/js/array/mjs/postcss.config.mjs
@@ -0,0 +1,18 @@
+import postcssImport from 'postcss-import'
+import postcssNested from 'postcss-nested'
+import cssnano from 'cssnano'
+
+export default function (ctx) {
+  return {
+    parser: ctx.parser ? 'sugarss' : false,
+    syntax: ctx.syntax ? 'sugarss' : false,
+    map: ctx.map ? 'inline' : false,
+    from: './test/js/array/fixtures/index.css',
+    to: './test/js/array/expect/index.css',
+    plugins: [
+      postcssImport(),
+      postcssNested(),
+      ctx.env === 'production' ? cssnano() : false
+    ]
+  }
+}
diff --git a/test/js/object/postcss.config.mjs b/test/js/object/postcss.config.mjs
new file mode 100644
index 0000000..18035ed
--- /dev/null
+++ b/test/js/object/postcss.config.mjs
@@ -0,0 +1,14 @@
+export default function (ctx) {
+  return {
+    parser: ctx.parser ? 'sugarss' : false,
+    syntax: ctx.syntax ? 'sugarss' : false,
+    map: ctx.map ? 'inline' : false,
+    from: './test/js/object/fixtures/index.css',
+    to: './test/js/object/expect/index.css',
+    plugins: {
+      'postcss-import': {},
+      'postcss-nested': {},
+      cssnano: ctx.env === 'production' ? {} : false
+    }
+  }
+}