diff --git a/packages/gitbook-core/package.json b/packages/gitbook-core/package.json
index 7aea7fbf6..a5f787ef3 100644
--- a/packages/gitbook-core/package.json
+++ b/packages/gitbook-core/package.json
@@ -12,6 +12,7 @@
     "immutable": "^3.8.1",
     "mousetrap": "1.6.0",
     "react": "^15.3.1",
+    "react-addons-css-transition-group": "^15.3.1",
     "react-dom": "^15.3.1",
     "react-helmet": "^3.1.0",
     "react-immutable-proptypes": "^2.1.0",
diff --git a/packages/gitbook-core/src/index.js b/packages/gitbook-core/src/index.js
index 7b7415058..3f0120c69 100644
--- a/packages/gitbook-core/src/index.js
+++ b/packages/gitbook-core/src/index.js
@@ -1,6 +1,7 @@
 require('whatwg-fetch');
 
 const React = require('react');
+const ReactCSSTransitionGroup = require('react-addons-css-transition-group');
 const Immutable = require('immutable');
 const Head = require('react-helmet');
 const Promise = require('bluebird');
@@ -66,6 +67,7 @@ module.exports = {
     PropTypes,
     // Librairies
     React,
+    ReactCSSTransitionGroup,
     Immutable,
     Promise
 };