diff --git a/src/Pane.js b/src/Pane.js
index 513015db..ea462a83 100644
--- a/src/Pane.js
+++ b/src/Pane.js
@@ -3,7 +3,7 @@ import PropTypes from 'prop-types';
 import Prefixer from 'inline-style-prefixer';
 import stylePropType from 'react-style-proptype';
 
-const USER_AGENT = 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.2 (KHTML, like Gecko) Safari/537.2';
+const USER_AGENT = typeof navigator !== 'undefined' ? navigator.userAgent : 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.2 (KHTML, like Gecko) Safari/537.2';
 
 class Pane extends React.Component {
     constructor(props) {
diff --git a/src/Resizer.js b/src/Resizer.js
index 463adb2a..61114714 100644
--- a/src/Resizer.js
+++ b/src/Resizer.js
@@ -3,7 +3,7 @@ import PropTypes from 'prop-types';
 import Prefixer from 'inline-style-prefixer';
 import stylePropType from 'react-style-proptype';
 
-const USER_AGENT = 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.2 (KHTML, like Gecko) Safari/537.2';
+const USER_AGENT = typeof navigator !== 'undefined' ? navigator.userAgent : 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.2 (KHTML, like Gecko) Safari/537.2';
 export const RESIZER_DEFAULT_CLASSNAME = 'Resizer';
 
 class Resizer extends React.Component {
diff --git a/src/SplitPane.js b/src/SplitPane.js
index 9aa5410f..084ca2f4 100644
--- a/src/SplitPane.js
+++ b/src/SplitPane.js
@@ -7,7 +7,7 @@ import stylePropType from 'react-style-proptype';
 import Pane from './Pane';
 import Resizer, { RESIZER_DEFAULT_CLASSNAME } from './Resizer';
 
-const USER_AGENT = 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.2 (KHTML, like Gecko) Safari/537.2';
+const USER_AGENT = typeof navigator !== 'undefined' ? navigator.userAgent : 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.2 (KHTML, like Gecko) Safari/537.2';
 
 function unFocus(document, window) {
     if (document.selection) {