diff --git a/src/libcore/lock.cpp b/src/libcore/lock.cpp
index 80dd2bb5..eeb8a568 100644
--- a/src/libcore/lock.cpp
+++ b/src/libcore/lock.cpp
@@ -74,12 +74,15 @@ bool ConditionVariable::wait(int ms) {
 
 		struct timespec ts;
 		ts.tv_sec = tv.tv_sec + ms/1000;
-		ts.tv_nsec = (tv.tv_usec + ms % 1000) * 1000;
-
+		ts.tv_nsec = tv.tv_usec * 1000 + (ms % 1000) * 1000000;
+		if (ts.tv_nsec >= 1000000000) {
+			ts.tv_nsec -= 1000000000;
+			ts.tv_sec++;
+		}
 		int retval = pthread_cond_timedwait(&m_cond, &m_mutex->m_mutex, &ts);
 #if defined(WIN32)
 		/* Should be outside of the switch statement (depending
-		   on the used compiler, the constants ETIMEDOUT and WSAETIMEDOUT
+		   on the used environment, the constants ETIMEDOUT and WSAETIMEDOUT
 		   are potentially identical */   
 		if (retval == WSAETIMEDOUT)
 			return false;
diff --git a/src/mtsgui/mainwindow.cpp b/src/mtsgui/mainwindow.cpp
index 05a1a669..698cb91c 100644
--- a/src/mtsgui/mainwindow.cpp
+++ b/src/mtsgui/mainwindow.cpp
@@ -163,12 +163,11 @@ MainWindow::MainWindow(QWidget *parent) :
 
 	connect(m_renderListener, SIGNAL(jobFinished(const RenderJob *, bool)), 
 		this, SLOT(onJobFinished(const RenderJob *, bool)), Qt::QueuedConnection);
-	connect(m_renderListener, SIGNAL(refresh(const RenderJob *, const Bitmap *)), 
-		this, SLOT(onRefresh(const RenderJob *, const Bitmap *)), Qt::BlockingQueuedConnection);
 	connect(m_renderListener, SIGNAL(workEnd(const RenderJob *, const ImageBlock *)), 
 		this, SLOT(onWorkEnd(const RenderJob *, const ImageBlock *)), Qt::DirectConnection);
 	connect(m_renderListener, SIGNAL(workBegin(const RenderJob *, const RectangularWorkUnit *, int)),
         this, SLOT(onWorkBegin(const RenderJob *, const RectangularWorkUnit *, int)), Qt::DirectConnection);
+	connect(m_renderListener, SIGNAL(refresh()), this, SLOT(onRefresh()), Qt::QueuedConnection);
 	connect(m_consoleAppender, 
 		SIGNAL(progressMessage(const RenderJob *, const QString &, float, const QString &)), 
 		this, SLOT(onProgressMessage(const RenderJob *, const QString &, float, const QString &)), 
@@ -1513,7 +1512,7 @@ void MainWindow::onJobFinished(const RenderJob *job, bool cancelled) {
 				ui->glView->resumePreview();
 		}
 	}
-	onRefresh(job, NULL);
+	refresh(job, NULL);
 	context->renderJob = NULL;
 	updateUI();
 	if (ui->tabBar->currentIndex() != -1 &&
@@ -1673,10 +1672,18 @@ void MainWindow::onWorkEnd(const RenderJob *job, const ImageBlock *block) {
 		emit updateView();
 }
 
-void MainWindow::onRefresh(const RenderJob *job, const Bitmap *_bitmap) {
+void MainWindow::onRefresh() {
+	const QRenderListener::RefreshRequest *req = m_renderListener->acquireRefreshRequest();
+	if (req)
+		refresh(req->first, req->second);
+	m_renderListener->releaseRefreshRequest();
+}
+
+void MainWindow::refresh(const RenderJob *job, const Bitmap *_bitmap) {
 	SceneContext *context = getContext(job, false);
 	if (context == NULL)
 		return;
+
 	Film *film = context->scene->getFilm();
 	Point2i co = film->getCropOffset();
 	Bitmap *bitmap = context->framebuffer;
diff --git a/src/mtsgui/mainwindow.h b/src/mtsgui/mainwindow.h
index bfd1c7a0..cc32f703 100644
--- a/src/mtsgui/mainwindow.h
+++ b/src/mtsgui/mainwindow.h
@@ -25,6 +25,10 @@
 
 #define MAX_RECENT_FILES 10
 
+// amount of time that a rendering thread will wait for the GUI to accept a
+// render view refresh request to show intermediate progress (in ms) 
+#define REFRESH_TIMEOUT 50
+
 namespace Ui {
     class MainWindow;
 }
@@ -41,6 +45,14 @@ class PreviewSettingsDlg;
 class QRenderListener : public QObject, public RenderListener {
 	Q_OBJECT
 public:
+	typedef std::pair<const RenderJob *, const Bitmap *> RefreshRequest;
+
+	QRenderListener() {
+		m_mutex = new Mutex();
+		m_cond = new ConditionVariable(m_mutex);
+		m_refreshRequest = NULL;
+	}
+
 	/// Called when work has begun in a rectangular image region
 	inline void workBeginEvent(const RenderJob *job, const RectangularWorkUnit *wu, int worker) {
 		emit workBegin(job, wu, worker);
@@ -50,10 +62,25 @@ public:
 	inline void workEndEvent(const RenderJob *job, const ImageBlock *wr) {
 		emit workEnd(job, wr);
 	}
+	
 
 	/// Called when the whole target image has been altered in some way
 	inline void refreshEvent(const RenderJob *job, const Bitmap *bitmap) {
-		emit refresh(job, bitmap);
+		m_mutex->lock();
+		RefreshRequest request = std::make_pair(job, bitmap);
+
+		/* Potentially overwrite a previous refresh request */
+		m_refreshRequest = &request;
+
+		/* Asynchronously signal the GUI */
+		emit refresh();
+
+		/* Wait for the GUI to draw the image (or another 
+		   thread to overwrite the refresh request) */
+		m_cond->wait(REFRESH_TIMEOUT);
+
+		m_refreshRequest = NULL;
+		m_mutex->unlock();
 	}
 
 	/// Called when a render job has completed successfully or unsuccessfully
@@ -61,14 +88,23 @@ public:
 		emit jobFinished(job, cancelled);
 	}
 
+	inline const RefreshRequest *acquireRefreshRequest() { m_mutex->lock(); return m_refreshRequest; }
+	inline void releaseRefreshRequest() { m_refreshRequest = NULL; m_cond->signal(); m_mutex->unlock(); }
+
 	MTS_DECLARE_CLASS()
 signals:
 	void workBegin(const RenderJob *job, const RectangularWorkUnit *wu, int worker);
 	void workEnd(const RenderJob *job, const ImageBlock *wr);
-	void refresh(const RenderJob *job, const Bitmap *bitmap);
 	void jobFinished(const RenderJob *job, bool cancelled);
+	void refresh();
+
 protected:
 	virtual ~QRenderListener() { }
+
+private:
+	ref<Mutex> m_mutex;
+	ref<ConditionVariable> m_cond;
+	RefreshRequest *m_refreshRequest;
 };
 
 class PreviewSettingsDialog;
@@ -97,6 +133,7 @@ protected:
 	void drawVisualWorkUnit(SceneContext *context, const VisualWorkUnit &block);
 	void checkForUpdates(bool notifyIfNone = false);
 	void saveAs(SceneContext *ctx, const QString &targetFile);
+	void refresh(const RenderJob *job, const Bitmap *bitmap);
 	QSize sizeHint() const;
 
 signals:
@@ -137,7 +174,7 @@ private slots:
 	void onClearRecent();
 	void onWorkBegin(const RenderJob *job, const RectangularWorkUnit *wu, int worker);
 	void onWorkEnd(const RenderJob *job, const ImageBlock *wr);
-	void onRefresh(const RenderJob *job, const Bitmap *bitmap);
+	void onRefresh();
 	void onJobFinished(const RenderJob *job, bool cancelled);
 	void onProgressMessage(const RenderJob *job, const QString &name, 
 		float progress, const QString &eta);