diff --git a/src/ShallowTraversal.js b/src/ShallowTraversal.js
index 350c4a1d4..7ecd4dafe 100644
--- a/src/ShallowTraversal.js
+++ b/src/ShallowTraversal.js
@@ -27,7 +27,7 @@ export function childrenOfNode(node) {
 
 export function hasClassName(node, className) {
   let classes = propsOfNode(node).className || '';
-  classes = classes.replace(/\s/g, ' ');
+  classes = String(classes).replace(/\s/g, ' ');
   return ` ${classes} `.indexOf(` ${className} `) > -1;
 }
 
diff --git a/test/ShallowTraversal-spec.js b/test/ShallowTraversal-spec.js
index f07dab051..0a667cd80 100644
--- a/test/ShallowTraversal-spec.js
+++ b/test/ShallowTraversal-spec.js
@@ -59,6 +59,12 @@ describe('ShallowTraversal', () => {
       expect(hasClassName(node, 'foo-bar')).to.equal(true);
     });
 
+    it('should work if className has a function in toString property', () => {
+      function classes() {}
+      classes.toString = () => 'foo-bar';
+      const node = (<div className={classes} />);
+      expect(hasClassName(node, 'foo-bar')).to.equal(true);
+    });
   });
 
   describe('nodeHasProperty', () => {