diff --git a/redo/reredo/control.c b/redo/reredo/control.c
index 22828a52..c713dc17 100644
--- a/redo/reredo/control.c
+++ b/redo/reredo/control.c
@@ -35,6 +35,13 @@ uintptr_t uiControlHandle(uiControl *c)
 	return (*(c->Handle))(c);
 }
 
+uiControl *uiControlParent(uiControl *c)
+{
+	struct controlBase *cb = controlBase(c);
+
+	return cb->parent;
+}
+
 static void controlUpdateState(uiControl *);
 
 void uiControlSetParent(uiControl *c, uiControl *parent)
diff --git a/redo/reredo/darwin/box.m b/redo/reredo/darwin/box.m
index 24dc7a6b..435738ea 100644
--- a/redo/reredo/darwin/box.m
+++ b/redo/reredo/darwin/box.m
@@ -190,6 +190,13 @@ static void relayout(uiBox *b)
 
 	[metrics release];
 	[views release];
+
+	uiDarwinControlRelayoutParent(uiControl(b));
+}
+
+static void boxRelayout(uiDarwinControl *c)
+{
+	relayout(uiBox(c));
 }
 
 void uiBoxAppend(uiBox *b, uiControl *c, int stretchy)
@@ -274,6 +281,7 @@ static uiBox *finishNewBox(BOOL vertical)
 	setHuggingPri(b->noStretchyView, NSLayoutPriorityDefaultLow, NSLayoutConstraintOrientationVertical);
 
 	uiDarwinFinishNewControl(b, uiBox);
+	uiDarwinControl(b)->Relayout = boxRelayout;
 
 	return b;
 }
diff --git a/redo/reredo/darwin/control.m b/redo/reredo/darwin/control.m
index 62bad8bc..b8cf3e74 100644
--- a/redo/reredo/darwin/control.m
+++ b/redo/reredo/darwin/control.m
@@ -10,6 +10,16 @@ uintmax_t uiDarwinControlType(void)
 	return type_uiDarwinControl;
 }
 
+void uiDarwinControlRelayoutParent(uiDarwinControl *c)
+{
+	uiControl *p;
+
+	p = uiControlParent(uiControl(c));
+	if (p == NULL)
+		return;
+	(*(uiDarwinControl(p)->Relayout))(p);
+}
+
 void osCommitShow(uiControl *c)
 {
 	NSView *view;
diff --git a/redo/reredo/ui.h b/redo/reredo/ui.h
index c629b8a4..f7b96635 100644
--- a/redo/reredo/ui.h
+++ b/redo/reredo/ui.h
@@ -61,6 +61,7 @@ _UI_EXTERN uintmax_t uiControlType(void);
 #define uiControl(this) ((uiControl *) uiIsA((this), uiControlType(), 1))
 _UI_EXTERN void uiControlDestroy(uiControl *);
 _UI_EXTERN uintptr_t uiControlHandle(uiControl *);
+_UI_EXTERN uiControl *uiControlParent(uiControl *);
 _UI_EXTERN void uiControlSetParent(uiControl *, uiControl *);
 _UI_EXTERN void uiControlShow(uiControl *);
 _UI_EXTERN void uiControlHide(uiControl *);
diff --git a/redo/reredo/ui_darwin.h b/redo/reredo/ui_darwin.h
index 92ac04ac..75bd2ed5 100644
--- a/redo/reredo/ui_darwin.h
+++ b/redo/reredo/ui_darwin.h
@@ -10,8 +10,12 @@ This file assumes that you have imported <Cocoa/Cocoa.h> and "ui.h" beforehand.
 typedef struct uiDarwinControl uiDarwinControl;
 struct uiDarwinControl {
 	uiControl c;
+	void (*Relayout)(uiControl *);
 };
 _UI_EXTERN uintmax_t uiDarwinControlType(void);
+#define uiDarwinControl(this) ((uiDarwinControl *) uiIsA((this), uiDarwinControlType(), 1))
+// TODO document
+_UI_EXTERN void uiDarwinControlRelayoutParent(uiDarwinControl *);
 
 // TODO document
 #define uiDarwinDefineControlWithOnDestroy(type, typefn, handlefield, onDestroy) \
@@ -35,6 +39,10 @@ _UI_EXTERN uintmax_t uiDarwinControlType(void);
 	static void _ ## type ## ContainerUpdateState(uiControl *c) \
 	{ \
 		/* do nothing */ \
+	} \
+	static void _ ## type ## Relayout(uiControl *c) \
+	{ \
+		uiDarwinControlRelayoutParent(uiDarwinControl(c)); \
 	}
 
 #define uiDarwinDefineControl(type, typefn, handlefield) \
@@ -44,6 +52,7 @@ _UI_EXTERN uintmax_t uiDarwinControlType(void);
 	uiControl(variable)->CommitDestroy = _ ## type ## CommitDestroy; \
 	uiControl(variable)->Handle = _ ## type ## Handle; \
 	uiControl(variable)->ContainerUpdateState = _ ## type ## ContainerUpdateState; \
+	uiDarwinControl(variable)->Relayout = _ ## type ## Relayout; \
 	uiDarwinFinishControl(uiControl(variable));
 
 // This is a function used to set up a control.