diff --git a/lib/class_builder.js b/lib/class_builder.js
index 868bef4..4c3eee6 100644
--- a/lib/class_builder.js
+++ b/lib/class_builder.js
@@ -745,18 +745,28 @@ function attachStatic( ctor, members, base, inheriting )
                 return base.$.apply( context, arguments );
             }
 
+            var prop_item = props[ found ][ prop ];
+
             // if a value was provided, this method should be treated as a
             // setter rather than a getter (we *must* test using
             // arguments.length to ensure that setting to undefined works)
             if ( arguments.length > 1 )
             {
-                props[ found ][ prop ] = val;
+                // if const, disallow modification
+                if ( prop_item[ 1 ][ 'const' ] )
+                {
+                    throw TypeError(
+                        "Cannot modify constant property '" + prop + "'"
+                    );
+                }
+
+                prop_item[ 0 ] = val;
                 return context;
             }
             else
             {
                 // return the value
-                return props[ found ][ prop ];
+                return prop_item[ 0 ];
             }
         } );
     }
diff --git a/lib/member_builder.js b/lib/member_builder.js
index b6d1803..ed14d2e 100644
--- a/lib/member_builder.js
+++ b/lib/member_builder.js
@@ -235,7 +235,7 @@ exports.buildProp = function( members, meta, name, value, keywords, base )
         );
     }
 
-    getMemberVisibility( members, keywords )[ name ] = value;
+    getMemberVisibility( members, keywords )[ name ] = [ value, keywords ];
 };
 
 
diff --git a/lib/propobj.js b/lib/propobj.js
index 42e7c6b..d4f7f04 100644
--- a/lib/propobj.js
+++ b/lib/propobj.js
@@ -137,7 +137,7 @@ function doSetup( dest, properties, methods, unless_keyword )
     {
         if ( hasOwn.call( properties, prop ) )
         {
-            dest[ prop ] = util.clone( properties[ prop ] );
+            dest[ prop ] = util.clone( properties[ prop ][ 0 ] );
         }
     }
 }
diff --git a/test/test-class_builder-const.js b/test/test-class_builder-const.js
index 59fd8de..b34d76a 100644
--- a/test/test-class_builder-const.js
+++ b/test/test-class_builder-const.js
@@ -103,3 +103,27 @@ var common  = require( './common' ),
     );
 } )();
 
+
+/**
+ * As the name implies, constant properties should not be writable.
+ */
+( function testConstKeywordCreatesImmutableProperty()
+{
+    try
+    {
+        // this should fail (trying to alter const prop foo)
+        builder.build( { 'const foo': 'bar'  } ).$( 'foo', 'baz' );
+    }
+    catch ( e )
+    {
+        assert.ok(
+            e.message.search( 'foo' ) !== -1,
+            "Const modification error should contain name of property"
+        );
+
+        return;
+    }
+
+    assert.fail( "Constant properties should not be writable" );
+} )();
+