diff --git a/lib/gradient.js b/lib/gradient.js
index 9252523..77daed2 100644
--- a/lib/gradient.js
+++ b/lib/gradient.js
@@ -7,7 +7,7 @@
 
   var api = {
     isGradient: function(bg) {
-      if (bg.startsWith('linear') || bg.startsWith('radial')) {
+      if (bg && (bg.startsWith('linear') || bg.startsWith('radial'))) {
         return true;
       } 
       return false;