diff --git a/src/CSSTransition.js b/src/CSSTransition.js
index df5e6a30..79c7cd8a 100644
--- a/src/CSSTransition.js
+++ b/src/CSSTransition.js
@@ -71,6 +71,9 @@ const removeClass = (node, classes) => node && classes && classes.split(' ').for
  * `*-active` classes represent which styles you want to animate **to**.
  */
 class CSSTransition extends React.Component {
+  static defaultProps = {
+    classNames: ''
+  }
   onEnter = (node, appearing) => {
     const { className } = this.getClassNames(appearing ? 'appear' : 'enter')
 
@@ -140,15 +143,17 @@ class CSSTransition extends React.Component {
 
   getClassNames = (type) => {
     const { classNames } = this.props;
+    const isStringClassNames = typeof classNames === 'string';
+    const prefix = isStringClassNames && classNames ? classNames + '-' : '';
 
-    let className = typeof classNames !== 'string' ?
-      classNames[type] : classNames + '-' + type;
+    let className = isStringClassNames ?
+      prefix + type : classNames[type]
 
-    let activeClassName = typeof classNames !== 'string' ?
-      classNames[type + 'Active'] : className + '-active';
+    let activeClassName = isStringClassNames ?
+      className + '-active' : classNames[type + 'Active'];
 
-    let doneClassName = typeof classNames !== 'string' ?
-      classNames[type + 'Done'] : className + '-done';
+    let doneClassName = isStringClassNames ?
+      className + '-done' : classNames[type + 'Done'];
 
     return {
       className,
diff --git a/test/CSSTransition-test.js b/test/CSSTransition-test.js
index b04fff16..2eb925e4 100644
--- a/test/CSSTransition-test.js
+++ b/test/CSSTransition-test.js
@@ -279,5 +279,38 @@ describe('CSSTransition', () => {
         }
       });
     });
+
+    it('should support empty prefix', done => {
+      let count = 0;
+
+      const instance = mount(
+        <CSSTransition
+          in
+          timeout={10}
+        >
+          <div/>
+        </CSSTransition>
+      )
+
+      instance.setProps({
+        in: false,
+
+        onExit(node){
+          count++;
+          expect(node.className).toEqual('exit');
+        },
+
+        onExiting(node){
+          count++;
+          expect(node.className).toEqual('exit exit-active');
+        },
+
+        onExited(node){
+          expect(node.className).toEqual('exit-done');
+          expect(count).toEqual(2);
+          done();
+        }
+      });
+    });
   });
 });