diff --git a/core/imagedownloader.cpp b/core/imagedownloader.cpp
index 2949d83d9..cbff1489c 100644
--- a/core/imagedownloader.cpp
+++ b/core/imagedownloader.cpp
@@ -140,7 +140,8 @@ QImage getHashedImage(const QString &file)
 	return res;
 }
 
-Thumbnailer::Thumbnailer()
+Thumbnailer::Thumbnailer() : failImage(QImage(":filter-close").scaled(maxThumbnailSize(), maxThumbnailSize(), Qt::KeepAspectRatio)), // TODO: Don't misuse filter close icon
+			     dummyImage(QImage(":photo-icon").scaled(maxThumbnailSize(), maxThumbnailSize(), Qt::KeepAspectRatio)) // TODO: Don't misuse photo-icon
 {
 	// Currently, we only process one image at a time. Stefan Fuchs reported problems when
 	// calculating multiple thumbnails at once and this hopefully helps.
@@ -200,16 +201,16 @@ static void addThumbnailToCache(const QImage &thumbnail, const QString &picture_
 	file.commit();
 }
 
-void Thumbnailer::processItem(QString filename, int size)
+void Thumbnailer::processItem(QString filename)
 {
 	QImage thumbnail = getThumbnailFromCache(filename);
 
 	if (thumbnail.isNull()) {
 		thumbnail = getHashedImage(filename);
 		if (thumbnail.isNull()) {
-			// TODO: Don't misuse filter close icon
-			thumbnail = QImage(":filter-close").scaled(size, size, Qt::KeepAspectRatio);
+			thumbnail = failImage;
 		} else {
+			int size = maxThumbnailSize();
 			thumbnail = thumbnail.scaled(size, size, Qt::KeepAspectRatio);
 			addThumbnailToCache(thumbnail, filename);
 		}
@@ -220,7 +221,7 @@ void Thumbnailer::processItem(QString filename, int size)
 	workingOn.remove(filename);
 }
 
-QImage Thumbnailer::fetchThumbnail(PictureEntry &entry, int size)
+QImage Thumbnailer::fetchThumbnail(PictureEntry &entry)
 {
 	QMutexLocker l(&lock);
 
@@ -228,9 +229,9 @@ QImage Thumbnailer::fetchThumbnail(PictureEntry &entry, int size)
 	const QString &filename = entry.filename;
 	if (!workingOn.contains(filename)) {
 		workingOn.insert(filename,
-				 QtConcurrent::run(&pool, [this, filename, size]() { processItem(filename, size); }));
+				 QtConcurrent::run(&pool, [this, filename]() { processItem(filename); }));
 	}
-	return QImage(":photo-icon").scaled(size, size, Qt::KeepAspectRatio);
+	return dummyImage;
 }
 
 void Thumbnailer::clearWorkQueue()
@@ -240,3 +241,27 @@ void Thumbnailer::clearWorkQueue()
 		it->cancel();
 	workingOn.clear();
 }
+
+static const int maxZoom = 3;	// Maximum zoom: thrice of standard size
+
+int Thumbnailer::defaultThumbnailSize()
+{
+	return defaultIconMetrics().sz_pic;
+}
+
+int Thumbnailer::maxThumbnailSize()
+{
+	return defaultThumbnailSize() * maxZoom;
+}
+
+int Thumbnailer::thumbnailSize(double zoomLevel)
+{
+	// Calculate size of thumbnails. The standard size is defaultIconMetrics().sz_pic.
+	// We use exponential scaling so that the central point is the standard
+	// size and the minimum and maximum extreme points are a third respectively
+	// three times the standard size.
+	// Naturally, these three zoom levels are then represented by
+	// -1.0 (minimum), 0 (standard) and 1.0 (maximum). The actual size is
+	// calculated as standard_size*3.0^zoomLevel.
+	return static_cast<int>(round(defaultThumbnailSize() * pow(maxZoom, zoomLevel)));
+}
diff --git a/core/imagedownloader.h b/core/imagedownloader.h
index d8e9d2d7d..92edea0b6 100644
--- a/core/imagedownloader.h
+++ b/core/imagedownloader.h
@@ -28,18 +28,23 @@ public:
 	// Schedule a thumbnail for fetching or calculation.
 	// Returns a placehlder thumbnail. The actual thumbnail will be sent
 	// via a signal later.
-	QImage fetchThumbnail(PictureEntry &entry, int size);
+	QImage fetchThumbnail(PictureEntry &entry);
 
 	// If we change dive, clear all unfinished thumbnail creations
 	void clearWorkQueue();
+	static int maxThumbnailSize();
+	static int defaultThumbnailSize();
+	static int thumbnailSize(double zoomLevel);
 signals:
 	void thumbnailChanged(QString filename, QImage thumbnail);
 private:
 	Thumbnailer();
-	void processItem(QString filename, int size);
+	void processItem(QString filename);
 
 	mutable QMutex lock;
 	QThreadPool pool;
+	QImage failImage;		// Shown when image-fetching fails
+	QImage dummyImage;		// Shown before thumbnail is fetched
 
 	QMap<QString,QFuture<void>> workingOn;
 };
diff --git a/qt-models/divepicturemodel.cpp b/qt-models/divepicturemodel.cpp
index c5453c3a9..89917761c 100644
--- a/qt-models/divepicturemodel.cpp
+++ b/qt-models/divepicturemodel.cpp
@@ -8,8 +8,6 @@
 
 #include <QFileInfo>
 
-static const int maxZoom = 3;	// Maximum zoom: thrice of standard size
-
 DivePictureModel *DivePictureModel::instance()
 {
 	static DivePictureModel *self = new DivePictureModel();
@@ -19,7 +17,7 @@ DivePictureModel *DivePictureModel::instance()
 DivePictureModel::DivePictureModel() : rowDDStart(0),
 				       rowDDEnd(0),
 				       zoomLevel(0.0),
-				       defaultSize(defaultIconMetrics().sz_pic)
+				       defaultSize(Thumbnailer::defaultThumbnailSize())
 {
 	connect(Thumbnailer::instance(), &Thumbnailer::thumbnailChanged,
 		this, &DivePictureModel::updateThumbnail, Qt::QueuedConnection);
@@ -47,22 +45,14 @@ void DivePictureModel::setZoomLevel(int level)
 
 void DivePictureModel::updateZoom()
 {
-	// Calculate size of thumbnails. The standard size is defaultIconMetrics().sz_pic.
-	// We use exponential scaling so that the central point is the standard
-	// size and the minimum and maximum extreme points are a third respectively
-	// three times the standard size.
-	// Naturally, these three zoom levels are then represented by
-	// -1.0 (minimum), 0 (standard) and 1.0 (maximum). The actual size is
-	// calculated as standard_size*3.0^zoomLevel.
-	size = static_cast<int>(round(defaultSize * pow(maxZoom, zoomLevel)));
+	size = Thumbnailer::thumbnailSize(zoomLevel);
 }
 
 void DivePictureModel::updateThumbnails()
 {
-	int maxSize = defaultSize * maxZoom;
 	updateZoom();
 	for (PictureEntry &entry: pictures)
-		entry.image = Thumbnailer::instance()->fetchThumbnail(entry, maxSize);
+		entry.image = Thumbnailer::instance()->fetchThumbnail(entry);
 }
 
 void DivePictureModel::updateDivePictures()
diff --git a/qt-models/divepicturemodel.h b/qt-models/divepicturemodel.h
index 0839630bd..e68c00570 100644
--- a/qt-models/divepicturemodel.h
+++ b/qt-models/divepicturemodel.h
@@ -31,8 +31,8 @@ private:
 	DivePictureModel();
 	QList<PictureEntry> pictures;
 	double zoomLevel;	// -1.0: minimum, 0.0: standard, 1.0: maximum
-	int defaultSize;
 	int size;
+	int defaultSize;
 	void updateThumbnails();
 	void updateZoom();
 };