diff --git a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift
index 4949e9989..605db2f06 100644
--- a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
+++ b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
@@ -95,9 +95,16 @@ class MachineDocument:
 	}
 
 	override func close() {
-		bestEffortUpdater.flush()
+		optionsPanel?.setIsVisible(false)
+		optionsPanel = nil
+
+		openGLView.delegate = nil
+		bestEffortUpdater.delegate = nil
+		bestEffortUpdater = nil
+
 		actionLock.lock()
 		drawLock.lock()
+		machine = nil
 		openGLView.invalidate()
 		openGLView.openGLContext!.makeCurrentContext()
 		actionLock.unlock()
diff --git a/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.h b/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.h
index 7130f3636..5bf76a152 100644
--- a/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.h	
+++ b/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.h	
@@ -22,7 +22,7 @@
 
 @property (nonatomic, assign) double clockRate;
 @property (nonatomic, assign) BOOL runAsUnlimited;
-@property (nonatomic, weak) id<CSBestEffortUpdaterDelegate> delegate;
+@property (atomic, weak) id<CSBestEffortUpdaterDelegate> delegate;
 
 - (void)update;
 - (void)flush;
diff --git a/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.m b/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.m
index eeb24c99e..67b44d18c 100644
--- a/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.m	
+++ b/OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.m	
@@ -20,6 +20,7 @@
 	NSTimeInterval _previousTimeInterval;
 	NSTimeInterval _cyclesError;
 	BOOL _hasSkipped;
+	id<CSBestEffortUpdaterDelegate> _delegate;
 }
 
 - (instancetype)init
@@ -35,15 +36,12 @@
 	return self;
 }
 
-- (void)update
-{
+- (void)update {
 	// Always post an -openGLView:didUpdateToTime: if a previous one isn't still ongoing. This is the hook upon which the substantial processing occurs.
-	if(!atomic_flag_test_and_set(&_updateIsOngoing))
-	{
+	if(!atomic_flag_test_and_set(&_updateIsOngoing)) {
 		dispatch_async(_serialDispatchQueue, ^{
 			NSTimeInterval timeInterval = [NSDate timeIntervalSinceReferenceDate];
-			if(_previousTimeInterval > DBL_EPSILON && timeInterval > _previousTimeInterval)
-			{
+			if(_previousTimeInterval > DBL_EPSILON && timeInterval > _previousTimeInterval) {
 				NSTimeInterval timeToRunFor = timeInterval - _previousTimeInterval;
 				double cyclesToRunFor = timeToRunFor * self.clockRate + _cyclesError;
 
@@ -52,24 +50,35 @@
 
 				// treat 'unlimited' as running at a factor of 10
 				if(self.runAsUnlimited) integerCyclesToRunFor *= 10;
-				[self.delegate bestEffortUpdater:self runForCycles:integerCyclesToRunFor didSkipPreviousUpdate:_hasSkipped];
+				[_delegate bestEffortUpdater:self runForCycles:integerCyclesToRunFor didSkipPreviousUpdate:_hasSkipped];
 			}
 			_previousTimeInterval = timeInterval;
 			_hasSkipped = NO;
 			atomic_flag_clear(&_updateIsOngoing);
 		});
-	}
-	else
-	{
+	} else {
 		dispatch_async(_serialDispatchQueue, ^{
 			_hasSkipped = YES;
 		});
 	}
 }
 
-- (void)flush
-{
+- (void)flush {
 	dispatch_sync(_serialDispatchQueue, ^{});
 }
 
+- (void)setDelegate:(id<CSBestEffortUpdaterDelegate>)delegate {
+	dispatch_sync(_serialDispatchQueue, ^{
+		_delegate = delegate;
+	});
+}
+
+- (id<CSBestEffortUpdaterDelegate>)delegate {
+	__block id<CSBestEffortUpdaterDelegate> delegate;
+	dispatch_sync(_serialDispatchQueue, ^{
+		delegate = _delegate;
+	});
+	return delegate;
+}
+
 @end