diff --git a/delegate_darwin.go b/delegate_darwin.go
index f6870e6..8d27281 100644
--- a/delegate_darwin.go
+++ b/delegate_darwin.go
@@ -19,6 +19,7 @@ This creates a class goAppDelegate that will be used as the delegate for /everyt
 // #include "objc_darwin.h"
 // extern void appDelegate_uitask(id, SEL, id);		/* from uitask_darwin.go */
 // extern BOOL appDelegate_windowShouldClose(id, SEL, id);
+// extern void appDelegate_windowDidResize(id, SEL, id);
 import "C"
 
 var (
@@ -32,6 +33,7 @@ const (
 var (
 	_uitask = sel_getUid("uitask:")
 	_windowShouldClose = sel_getUid("windowShouldClose:")
+	_windowDidResize = sel_getUid("windowDidResize:")
 )
 
 func mkAppDelegate() error {
@@ -49,6 +51,11 @@ func mkAppDelegate() error {
 	if err != nil {
 		return fmt.Errorf("error adding NSApplication delegate windowShouldClose: method (to handle window close button events): %v", err)
 	}
+	err = addDelegateMethod(appdelegateclass, _windowDidResize,
+		C.appDelegate_windowDidResize, delegate_void)
+	if err != nil {
+		return fmt.Errorf("error adding NSApplication delegate windowDidResize: method (to handle window resize events): %v", err)
+	}
 	// TODO using objc_new() causes a segfault; find out why
 	// TODO make alloc followed by init (I thought NSObject provided its own init?)
 	appDelegate = objc_alloc(objc_getClass(_goAppDelegate))
@@ -62,6 +69,23 @@ func appDelegate_windowShouldClose(self C.id, sel C.SEL, win C.id) C.BOOL {
 	return C.BOOL(C.NO)		// don't close
 }
 
+var (
+	_object = sel_getUid("object")
+)
+
+//export appDelegate_windowDidResize
+func appDelegate_windowDidResize(self C.id, sel C.SEL, notification C.id) {
+	win := C.objc_msgSend_noargs(notification, _object)
+	sysData := getSysData(win)
+	r := C.objc_msgSend_stret_rect_noargs(win, _frame)
+	if sysData.resize != nil {
+		err := sysData.resize(int(r.x), int(r.y), int(r.width), int(r.height))
+		if err != nil {
+			panic("child resize failed: " + err.Error())
+		}
+	}
+}
+
 // this actually constructs the delegate class
 
 var (
diff --git a/prefsize_darwin.go b/prefsize_darwin.go
index 316662e..630969e 100644
--- a/prefsize_darwin.go
+++ b/prefsize_darwin.go
@@ -15,6 +15,7 @@ var (
 )
 
 func (s *sysData) preferredSize() (width int, height int) {
+if classTypes[s.ctype].make == nil { return 0, 0 }	// prevent lockup during window resize
 	cell := C.objc_msgSend_noargs(s.id, _cell)
 	cs := C.objc_msgSend_stret_size_noargs(cell, _cellSize)
 	return int(cs.width), int(cs.height)