diff --git a/.npmignore b/.npmignore
index e8add85..ad29248 100755
--- a/.npmignore
+++ b/.npmignore
@@ -1,4 +1,3 @@
-src
 tests
 coverage
 .*
diff --git a/package.json b/package.json
index 9a49f02..3cb7bf1 100644
--- a/package.json
+++ b/package.json
@@ -45,6 +45,7 @@
   "scripts": {
     "lint": "eslint ./src ./tests",
     "test": "mocha --compilers js:babel-register ./tests/**/*.js",
+    "postinstall": "npm install --ignore-scripts && babel ./src --out-dir ./dist",
     "build": "babel ./src --out-dir ./dist"
   }
 }
diff --git a/src/generateAppendClassName.js b/src/generateAppendClassName.js
index c896f6e..cdc97ad 100644
--- a/src/generateAppendClassName.js
+++ b/src/generateAppendClassName.js
@@ -4,6 +4,7 @@ const stylesIndex = new Map();
 
 export default (styles, styleNames: Array<string>, errorWhenNotFound: boolean): string => {
     let appendClassName,
+        key,
         stylesIndexMap;
 
     stylesIndexMap = stylesIndex.get(styles);
@@ -15,7 +16,14 @@ export default (styles, styleNames: Array<string>, errorWhenNotFound: boolean):
             return styleNameIndex;
         }
     } else {
-        stylesIndexMap = stylesIndex.set(styles, new Map());
+        stylesIndex.set(styles, new Map());
+        stylesIndexMap = new Map();
+
+        for (key in stylesIndex) {
+            if (stylesIndex.hasOwnProperty(key)) {
+                stylesIndexMap.set(key, stylesIndex[key]);
+            }
+        }
     }
 
     appendClassName = '';