diff --git a/AppKit/CPWindow/CPWindow.j b/AppKit/CPWindow/CPWindow.j
index 5859f6443..1b0171c38 100644
--- a/AppKit/CPWindow/CPWindow.j
+++ b/AppKit/CPWindow/CPWindow.j
@@ -338,6 +338,7 @@ CPTexturedBackgroundWindowMask
         _isSheet = NO;
         _sheetContext = nil;
         _parentView = nil;
+        _frameAnimation = nil;
         _frameAnimationDelegate = nil;
 
         // Set up our window number.