diff --git a/AppKit/CPWindow/CPWindow.j b/AppKit/CPWindow/CPWindow.j
index 90917f81e..4a02eae68 100644
--- a/AppKit/CPWindow/CPWindow.j
+++ b/AppKit/CPWindow/CPWindow.j
@@ -1815,7 +1815,7 @@ CPTexturedBackgroundWindowMask
 /*!
     Returns \c YES if the window can be moved.
 */
-- (void)isMovable
+- (BOOL)isMovable
 {
     return _isMovable;
 }