diff --git a/gulpfile.js b/gulpfile.js
index 315c34de4..5f0ce0fc6 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -21,7 +21,9 @@ gulp.task('build', function () {
     .pipe(webpack({
       config: [
         require('./support/webpack.config.js'),
-        require('./support/webpack.config.slim.js')
+        require('./support/webpack.config.dev.js'),
+        require('./support/webpack.config.slim.js'),
+        require('./support/webpack.config.slim.dev.js')
       ]
     }))
     .pipe(gulp.dest(BUILD_TARGET_DIR));
diff --git a/package.json b/package.json
index 2341e0c35..2d7c4a92c 100644
--- a/package.json
+++ b/package.json
@@ -51,6 +51,7 @@
     "socket.io": "2.0.4",
     "strip-loader": "0.1.2",
     "text-blob-builder": "0.0.1",
+    "webpack-merge": "4.1.2",
     "webpack-stream": "3.2.0",
     "zuul": "^3.11.1  ",
     "zuul-builder-webpack": "^1.2.0",
diff --git a/support/webpack.config.dev.js b/support/webpack.config.dev.js
new file mode 100644
index 000000000..23508f480
--- /dev/null
+++ b/support/webpack.config.dev.js
@@ -0,0 +1,39 @@
+
+var webpack = require('webpack');
+
+module.exports = {
+  name: 'default',
+  entry: './lib/index.js',
+  output: {
+    library: 'io',
+    libraryTarget: 'umd',
+    filename: 'socket.io.dev.js'
+  },
+  externals: {
+    global: glob()
+  },
+  devtool: 'source-map',
+  module: {
+    loaders: [{
+      test: /\.js$/,
+      exclude: /(node_modules|bower_components)/,
+      loader: 'babel', // 'babel-loader' is also a legal name to reference
+      query: { presets: ['es2015'] }
+    }, {
+      test: /\json3.js/,
+      loader: 'imports?define=>false'
+    }]
+  }
+};
+
+/**
+ * Populates `global`.
+ *
+ * @api private
+ */
+
+function glob () {
+  return 'typeof self !== "undefined" ? self : ' +
+    'typeof window !== "undefined" ? window : ' +
+    'typeof global !== "undefined" ? global : {}';
+}
diff --git a/support/webpack.config.js b/support/webpack.config.js
index 26cf99d7c..42a48e316 100644
--- a/support/webpack.config.js
+++ b/support/webpack.config.js
@@ -1,18 +1,13 @@
-
 var webpack = require('webpack');
+var merge = require('webpack-merge');
+var baseConfig = require('./webpack.config.dev.js')
 
-module.exports = {
-  name: 'default',
-  entry: './lib/index.js',
+module.exports = merge(baseConfig, {
   output: {
     library: 'io',
     libraryTarget: 'umd',
     filename: 'socket.io.js'
   },
-  externals: {
-    global: glob()
-  },
-  devtool: 'source-map',
   plugins: [
     new webpack.optimize.UglifyJsPlugin({
       compress: {
@@ -27,27 +22,4 @@ module.exports = {
       }
     })
   ],
-  module: {
-    loaders: [{
-      test: /\.js$/,
-      exclude: /(node_modules|bower_components)/,
-      loader: 'babel', // 'babel-loader' is also a legal name to reference
-      query: { presets: ['es2015'] }
-    }, {
-      test: /\json3.js/,
-      loader: 'imports?define=>false'
-    }]
-  }
-};
-
-/**
- * Populates `global`.
- *
- * @api private
- */
-
-function glob () {
-  return 'typeof self !== "undefined" ? self : ' +
-    'typeof window !== "undefined" ? window : ' +
-    'typeof global !== "undefined" ? global : {}';
-}
+});
diff --git a/support/webpack.config.slim.dev.js b/support/webpack.config.slim.dev.js
new file mode 100644
index 000000000..805730992
--- /dev/null
+++ b/support/webpack.config.slim.dev.js
@@ -0,0 +1,46 @@
+
+var webpack = require('webpack');
+
+module.exports = {
+  name: 'slim',
+  entry: './lib/index.js',
+  output: {
+    library: 'io',
+    libraryTarget: 'umd',
+    filename: 'socket.io.slim.dev.js'
+  },
+  externals: {
+    global: glob(),
+    json3: 'JSON'
+  },
+  devtool: 'source-map',
+  plugins: [
+    new webpack.NormalModuleReplacementPlugin(/debug/, process.cwd() + '/support/noop.js'),
+  ],
+  module: {
+    loaders: [{
+      test: /\.js$/,
+      exclude: /(node_modules|bower_components)/,
+      loader: 'babel', // 'babel-loader' is also a legal name to reference
+      query: { presets: ['es2015'] }
+    }, {
+      test: /\json3.js/,
+      loader: 'imports?define=>false'
+    }, {
+      test: /\.js$/,
+      loader: 'strip-loader?strip[]=debug'
+    }]
+  }
+};
+
+/**
+ * Populates `global`.
+ *
+ * @api private
+ */
+
+function glob () {
+  return 'typeof self !== "undefined" ? self : ' +
+    'typeof window !== "undefined" ? window : ' +
+    'typeof global !== "undefined" ? global : {}';
+}
diff --git a/support/webpack.config.slim.js b/support/webpack.config.slim.js
index 0a68023d4..2c92b3305 100644
--- a/support/webpack.config.slim.js
+++ b/support/webpack.config.slim.js
@@ -1,47 +1,14 @@
-
 var webpack = require('webpack');
+var merge = require('webpack-merge');
+var baseConfig = require('./webpack.config.slim.dev.js')
 
-module.exports = {
-  name: 'slim',
-  entry: './lib/index.js',
+module.exports = merge(baseConfig, {
   output: {
     library: 'io',
     libraryTarget: 'umd',
     filename: 'socket.io.slim.js'
   },
-  externals: {
-    global: glob(),
-    json3: 'JSON'
-  },
-  devtool: 'source-map',
   plugins: [
-    new webpack.NormalModuleReplacementPlugin(/debug/, process.cwd() + '/support/noop.js'),
     new webpack.optimize.UglifyJsPlugin()
   ],
-  module: {
-    loaders: [{
-      test: /\.js$/,
-      exclude: /(node_modules|bower_components)/,
-      loader: 'babel', // 'babel-loader' is also a legal name to reference
-      query: { presets: ['es2015'] }
-    }, {
-      test: /\json3.js/,
-      loader: 'imports?define=>false'
-    }, {
-      test: /\.js$/,
-      loader: 'strip-loader?strip[]=debug'
-    }]
-  }
-};
-
-/**
- * Populates `global`.
- *
- * @api private
- */
-
-function glob () {
-  return 'typeof self !== "undefined" ? self : ' +
-    'typeof window !== "undefined" ? window : ' +
-    'typeof global !== "undefined" ? global : {}';
-}
+});