diff --git a/lib/ClassBuilder.js b/lib/ClassBuilder.js
index fb657c8..532b70f 100644
--- a/lib/ClassBuilder.js
+++ b/lib/ClassBuilder.js
@@ -230,6 +230,11 @@ exports.isInstanceOf = function( type, instance )
 {
     var meta, implemented, i;
 
+    if ( !( type && instance ) )
+    {
+        return false;
+    }
+
     try
     {
         // check prototype chain (will throw an error if type is not a
diff --git a/test/test-class.js b/test/test-class.js
index 5c76b4f..b8a4a07 100644
--- a/test/test-class.js
+++ b/test/test-class.js
@@ -102,6 +102,16 @@ assert.ok(
     "Class instance is recognized by Class.isInstanceOf()"
 );
 
+assert.ok(
+    Class.isInstanceOf( Foo, undefined ) === false,
+    "Checking instance of undefined will not throw an error"
+);
+
+assert.ok(
+    Class.isInstanceOf( undefined, {} ) === false,
+    "Checking for instance of undefined will not throw an error"
+);
+
 assert.ok(
     !( Class.isInstanceOf( Foo, Foo ) ),
     "Class is not an instance of itself when uninstantiated"