diff --git a/enums.js b/enums.js
index 560ae4b..06734fc 100644
--- a/enums.js
+++ b/enums.js
@@ -6,7 +6,7 @@
         });
         return target;
     }
-    
+
     function Symbol(name, props) {
         this.name = name;
         if (props) {
@@ -46,10 +46,10 @@
         );
     }
     Enum.prototype.contains = function(sym) {
-        if (! sym instanceof Symbol) return false;
+        if (!(sym instanceof Symbol)) return false;
         return this[sym.name] === sym;
     }
     exports.Enum = Enum;
     exports.Symbol = Symbol;
 }(typeof exports === "undefined" ? this.enums = {} : exports));
-// Explanation of this pattern: http://www.2ality.com/2011/08/universal-modules.html
\ No newline at end of file
+// Explanation of this pattern: http://www.2ality.com/2011/08/universal-modules.html
diff --git a/enums.spec.js b/enums.spec.js
index 57d7ba8..59b6646 100644
--- a/enums.spec.js
+++ b/enums.spec.js
@@ -17,6 +17,7 @@ describe("Enum", function() {
         var fruit = new enums.Enum("apple", "banana");
         expect(color.contains(color.red)).toBeTruthy();
         expect(color.contains(fruit.apple)).toBeFalsy();
+        expect(color.contains(undefined)).toBeFalsy();
     });
 });