diff --git a/lib/class.js b/lib/class.js
index 55cca98..67c4bd9 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -22,12 +22,24 @@
  * @package core
  */
 
-// whether getters/setters are supported
+/**
+ * Whether getters/setters are supported
+ * @var  {boolean}
+ */
 var getset = ( Object.prototype.__defineGetter__ === undefined )
     ? false
     : true
 ;
 
+/**
+ * Whether the Object.freeze() method is available
+ * @var  {boolean}
+ */
+var can_freeze = ( Object.seal === undefined )
+    ? false
+    : true
+;
+
 
 /**
  * Creates a class, inheriting either from the provided base class or the
@@ -133,6 +145,13 @@ var extend = ( function( extending )
         new_class.prototype   = prototype;
         new_class.constructor = new_class;
 
+        // lock down the new class (if supported) to ensure that we can't add
+        // members at runtime
+        if ( can_freeze )
+        {
+            Object.freeze( new_class );
+        }
+
         // we're done with the extension process
         extending = false;
 
diff --git a/test/test-class.js b/test/test-class.js
index 5281122..1e29952 100644
--- a/test/test-class.js
+++ b/test/test-class.js
@@ -34,7 +34,10 @@ assert.ok(
 );
 
 
-var Foo = Class.extend();
+var Foo = Class.extend(
+{
+    value: 'foo',
+});
 
 
 assert.ok(
@@ -42,3 +45,8 @@ assert.ok(
     "Extend method creates a new object"
 );
 
+assert.equal(
+    Object.isFrozen( Foo ),
+    true,
+    "Generated class should be frozen"
+);