diff --git a/src/file-io/collection.h b/src/file-io/collection.h
--- a/src/file-io/collection.h
+++ b/src/file-io/collection.h
@@ -20,6 +20,8 @@
 #define PALAPELI_COLLECTION_H
 
 #include <QStandardItemModel>
+#include <QMutex>
+
 class KConfig;
 class KConfigGroup;
 
@@ -56,6 +58,7 @@
 
 			KConfig* m_config;
 			KConfigGroup* m_group;
+			QMutex m_configMutex;
 	};
 }
 
diff --git a/src/file-io/collection.cpp b/src/file-io/collection.cpp
--- a/src/file-io/collection.cpp
+++ b/src/file-io/collection.cpp
@@ -129,7 +129,7 @@
 		//construct puzzle with CollectionStorageComponent
 		if (!path.isEmpty() && (desktopPath.isEmpty() || QFileInfo(path).lastModified() >= QFileInfo(desktopPath).lastModified()))
 		{
-			Palapeli::Puzzle* puzzle = new Palapeli::Puzzle(new Palapeli::CollectionStorageComponent(puzzleGroup), path, puzzleId);
+			Palapeli::Puzzle* puzzle = new Palapeli::Puzzle(new Palapeli::CollectionStorageComponent(puzzleGroup, &m_configMutex), path, puzzleId);
 			appendRow(new Item(puzzle));
 			continue;
 		}
@@ -176,9 +176,11 @@
 	puzzle->get(Palapeli::PuzzleComponent::ArchiveStorage).waitForFinished();
 	//create the config group for this puzzle (use pseudo-URL to avoid problems
 	//when the configuration directory is moved)
+	m_configMutex.lock();
 	KConfigGroup puzzleGroup(m_group, id);
 	puzzleGroup.writeEntry("Location", palapeliUrl);
 	m_config->sync();
+	m_configMutex.unlock();
 	//add to the model
 	appendRow(new Item(puzzle));
 }
@@ -217,8 +219,10 @@
 	if (!QFile(puzzle->location()).remove())
 		return false;
 	//remove puzzle from config
+	m_configMutex.lock();
 	KConfigGroup(m_group, puzzle->identifier()).deleteGroup();
 	m_config->sync();
+	m_configMutex.unlock();
 	//remove puzzle from model and delete it
 	const int count = rowCount();
 	for (int row = 0; row < count; ++row)
diff --git a/src/file-io/components-collectionstorage.cpp b/src/file-io/components-collectionstorage.cpp
--- a/src/file-io/components-collectionstorage.cpp
+++ b/src/file-io/components-collectionstorage.cpp
@@ -21,9 +21,10 @@
 #include <QtCore/QBuffer>
 #include <QtCore/QFileInfo>
 #include <KConfigGroup>
+#include <QThread>
 
-Palapeli::CollectionStorageComponent::CollectionStorageComponent(KConfigGroup* group)
-	: m_group(group)
+Palapeli::CollectionStorageComponent::CollectionStorageComponent(KConfigGroup* group, QMutex *groupMutex)
+	: m_group(group), m_groupMutex(groupMutex)
 {
 }
 
@@ -45,6 +46,7 @@
 	}
 	//try to serve metadata from cache
 	const QDateTime mtime = QFileInfo(file).lastModified();
+	m_groupMutex->lock();
 	if (m_group->readEntry("ModifyDateTime", QDateTime()) == mtime)
 	{
 		//cache is up-to-date
@@ -55,10 +57,12 @@
 		metadata.pieceCount = m_group->readEntry("PieceCount", 0);
 		metadata.modifyProtection = m_group->readEntry("ModifyProtection", false);
 		metadata.thumbnail.loadFromData(m_group->readEntry("Thumbnail", QByteArray()));
+		m_groupMutex->unlock();
 		return new Palapeli::MetadataComponent(metadata);
 	}
 	else
 	{
+		m_groupMutex->unlock();
 		//read metadata from archive...
 		const Palapeli::PuzzleComponent* arStorage = puzzle()->get(ArchiveStorage);
 		if (!arStorage)
@@ -69,16 +73,18 @@
 		//...and populate cache (image is written via a buffer
 		//because KConfig does not support QImage directly)
 		const Palapeli::PuzzleMetadata metadata = dynamic_cast<Palapeli::MetadataComponent*>(cMetadata)->metadata;
+		QBuffer buffer;
+		metadata.thumbnail.save(&buffer, "PNG");
+		m_groupMutex->lock();
 		m_group->writeEntry("Name", metadata.name);
 		m_group->writeEntry("Comment", metadata.comment);
 		m_group->writeEntry("Author", metadata.author);
 		m_group->writeEntry("PieceCount", metadata.pieceCount);
 		m_group->writeEntry("ModifyProtection", metadata.modifyProtection);
 		m_group->writeEntry("ModifyDateTime", mtime);
-		QBuffer buffer;
-		metadata.thumbnail.save(&buffer, "PNG");
 		m_group->writeEntry("Thumbnail", buffer.data());
 		m_group->sync();
+		m_groupMutex->unlock();
 		return cMetadata;
 	}
 }
diff --git a/src/file-io/components.h b/src/file-io/components.h
--- a/src/file-io/components.h
+++ b/src/file-io/components.h
@@ -106,12 +106,13 @@
 		COMPONENT_SUBCLASS(CollectionStorage)
 		public:
 			///Takes ownership of @a group.
-			CollectionStorageComponent(KConfigGroup* group);
+			CollectionStorageComponent(KConfigGroup* group, QMutex *groupMutex);
 			virtual ~CollectionStorageComponent();
 
 			Palapeli::PuzzleComponent* cast(Type type) const Q_DECL_OVERRIDE;
 		private:
 			KConfigGroup* m_group;
+			QMutex *m_groupMutex;
 	};
 
 	///This is used by the collection if, instead of an actual puzzle archive,