diff --git a/lib/class.js b/lib/class.js
index 9a86c13..cfae254 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -794,9 +794,17 @@ function attachPropInit( prototype, properties, members )
             this, class_instance[ this.__iid ], properties[ 'public' ]
         );
 
+        // use whatever was returned by the property proxy (which may not be a
+        // proxy, depending on JS engine support)
         class_instance[ this.__iid ] = inst_props;
 
-        propobj.setup( inst_props, properties, members );
+        // if we're inheriting, perform a setup that doesn't include everything
+        // that we don't want (e.g. private properties)
+        var setup = ( inherit )
+            ? propobj.setupInherited
+            : propobj.setup
+        ;
+        setup( inst_props, properties, members );
     });
 }
 
diff --git a/test/test-class-visibility.js b/test/test-class-visibility.js
index bf28361..c535a75 100644
--- a/test/test-class-visibility.js
+++ b/test/test-class-visibility.js
@@ -36,7 +36,7 @@ var common  = require( './common' ),
     privf = function() { return priv; },
 
     // new anonymous class instance
-    foo = Class.extend( {
+    Foo = Class.extend( {
         'public pub':      pub,
         'protected peeps': prot,
         'private parts':   priv,
@@ -60,7 +60,14 @@ var common  = require( './common' ),
         {
             this[ name ] = value;
         },
-    })();
+    }),
+
+    // instance of Foo
+    foo = Foo(),
+
+    // subtype
+    sub_foo = Foo.extend( {} )()
+;
 
 
 /**
@@ -220,3 +227,52 @@ var common  = require( './common' ),
     );
 } )();
 
+
+/**
+ * Inheritance 101; protected members should be available to subtypes
+ */
+( function testProtectedMembersAreInheritedFromParent()
+{
+    assert.equal(
+        sub_foo.getProp( 'peeps' ),
+        prot,
+        "Protected properties are available to subtypes"
+    );
+
+    // invoke rather than checking for equality, because the method may be
+    // wrapped
+    assert.equal(
+        sub_foo.getProp( 'protf' )(),
+        prot,
+        "Protected methods are available to subtypes"
+    );
+} )();
+
+
+/**
+ * Interface 101-2: We do not want private members to be available to subtypes.
+ */
+( function testPrivateMembersOfSupertypesAreInaccessibleToSubtypes()
+{
+    // browsers that do not support the property proxy will not support
+    // encapsulating properties
+    if ( !( propobj.supportsPropProxy() ) )
+    {
+        return;
+    }
+
+    assert.equal(
+        sub_foo.getProp( 'parts' ),
+        undefined,
+        "Private properties of supertypes should be unavailable to subtypes"
+    );
+
+    // invoke rather than checking for equality, because the method may be
+    // wrapped
+    assert.equal(
+        sub_foo.getProp( 'privf' ),
+        undefined,
+        "Private methods of supertypes should be unavailable to subtypes"
+    );
+} )();
+