diff --git a/src/private/externalpartstorage.cpp b/src/private/externalpartstorage.cpp
index d11f6f81b..97611a241 100644
--- a/src/private/externalpartstorage.cpp
+++ b/src/private/externalpartstorage.cpp
@@ -1,337 +1,337 @@
 /*
  * Copyright (C) 2015  Daniel Vrátil <dvratil@redhat.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
 
 #include "externalpartstorage_p.h"
 #include "standarddirs_p.h"
 #include "akonadiprivate_debug.h"
 
 #include <QDir>
 #include <QFileInfo>
 #include <QMutexLocker>
 #include <QThread>
 
 using namespace Akonadi;
 
 ExternalPartStorage *ExternalPartStorage::sInstance = nullptr;
 
 ExternalPartStorageTransaction::ExternalPartStorageTransaction()
 {
     ExternalPartStorage::self()->beginTransaction();
 }
 
 ExternalPartStorageTransaction::~ExternalPartStorageTransaction()
 {
     if (ExternalPartStorage::self()->inTransaction()) {
         rollback();
     }
 }
 
 bool ExternalPartStorageTransaction::commit()
 {
     return ExternalPartStorage::self()->commitTransaction();
 }
 
 bool ExternalPartStorageTransaction::rollback()
 {
     return ExternalPartStorage::self()->rollbackTransaction();
 }
 
 ExternalPartStorage::ExternalPartStorage()
 {
 }
 
 ExternalPartStorage *ExternalPartStorage::self()
 {
     static QMutex instanceLock;
     QMutexLocker locker(&instanceLock);
     if (!sInstance) {
         sInstance = new ExternalPartStorage();
     }
     return sInstance;
 }
 
 QString ExternalPartStorage::resolveAbsolutePath(const QByteArray &filename, bool *exists, bool legacyFallback)
 {
     return resolveAbsolutePath(QString::fromLocal8Bit(filename), exists, legacyFallback);
 }
 
 QString ExternalPartStorage::resolveAbsolutePath(const QString &filename, bool *exists, bool legacyFallback)
 {
     if (exists) {
         *exists = false;
     }
 
     QFileInfo finfo(filename);
     if (finfo.isAbsolute()) {
         if (exists && finfo.exists()) {
             *exists = true;
         }
         return filename;
     }
 
     const QString basePath = StandardDirs::saveDir("data", QStringLiteral("file_db_data"));
     Q_ASSERT(!basePath.isEmpty());
 
     // Part files are stored in levelled cache. We use modulo 100 of the partID
     // to ensure even distribution of the part files into the subfolders.
     // PartID is encoded in filename as "PARTID_rX".
     const int revPos = filename.indexOf(QLatin1Char('_'));
     const QString path = basePath
                          + QDir::separator()
                          + (revPos > 1 ? filename[revPos - 2] : QLatin1Char('0'))
-                         + filename[revPos - 1]
+                         + (revPos > 0 ? filename[revPos - 1] : QLatin1Char('0'))
                          + QDir::separator()
                          + filename;
     // If legacy fallback is disabled, return it in any case
     if (!legacyFallback) {
         QFileInfo finfo(path);
         QDir().mkpath(finfo.path());
         return path;
     }
 
     // ..otherwise return it only if it exists
     if (QFile::exists(path)) {
         if (exists) {
             *exists = true;
         }
         return path;
     }
 
     // .. and fallback to legacy if it does not, but only when legacy exists
     const QString legacyPath = basePath + QDir::separator() + filename;
     if (QFile::exists(legacyPath)) {
         if (exists) {
             *exists = true;
         }
         return legacyPath;
     } else {
         QFileInfo finfo(path);
         QDir().mkpath(finfo.path());
         // If neither legacy or new path exists, return the new path, so that
         // new items are created in the correct location
         return path;
     }
 }
 
 bool ExternalPartStorage::createPartFile(const QByteArray &data, qint64 partId,
         QByteArray &partFileName)
 {
     bool exists = false;
     partFileName = updateFileNameRevision(QByteArray::number(partId));
     const QString path = resolveAbsolutePath(partFileName, &exists);
     if (exists) {
         qCWarning(AKONADIPRIVATE_LOG) << "Error: asked to create a part" << partFileName << ", which already exists!";
         return false;
     }
 
     QFile f(path);
     if (!f.open(QIODevice::WriteOnly)) {
         qCWarning(AKONADIPRIVATE_LOG) << "Error: failed to open new part file for writing:" << f.errorString();
         return false;
     }
     if (f.write(data) != data.size()) {
         // TODO: Maybe just try again?
         qCWarning(AKONADIPRIVATE_LOG) << "Error: failed to write all data into the part file";
         return false;
     }
     f.close();
 
     if (inTransaction()) {
         addToTransaction({ { Operation::Create, path } });
     }
     return true;
 }
 
 bool ExternalPartStorage::updatePartFile(const QByteArray &newData, const QByteArray &partFile,
         QByteArray &newPartFile)
 {
     bool exists = false;
     const QString currentPartPath = resolveAbsolutePath(partFile, &exists);
     if (!exists) {
         qCWarning(AKONADIPRIVATE_LOG) << "Error: asked to update a non-existent part, aborting update";
         return false;
     }
 
     newPartFile = updateFileNameRevision(partFile);
     exists = false;
     const QString newPartPath = resolveAbsolutePath(newPartFile, &exists);
     if (exists) {
         qCWarning(AKONADIPRIVATE_LOG) << "Error: asked to update part" << partFile << ", but" << newPartFile << "already exists, aborting update";
         return false;
     }
 
     QFile f(newPartPath);
     if (!f.open(QIODevice::WriteOnly)) {
         qCWarning(AKONADIPRIVATE_LOG) << "Error: failed to open new part file for update:" << f.errorString();
         return false;
     }
 
     if (f.write(newData) != newData.size()) {
         // TODO: Maybe just try again?
         qCWarning(AKONADIPRIVATE_LOG) << "Error: failed to write all data into the part file";
         return false;
     }
     f.close();
 
     if (inTransaction()) {
         addToTransaction({ { Operation::Create, newPartPath },
             { Operation::Delete, currentPartPath }
         });
     } else {
         if (!QFile::remove(currentPartPath)) {
             // Not a reason to fail the operation
             qCWarning(AKONADIPRIVATE_LOG) << "Error: failed to remove old part payload file" << currentPartPath;
         }
     }
 
     return true;
 }
 
 bool ExternalPartStorage::removePartFile(const QString &partFile)
 {
     if (inTransaction()) {
         addToTransaction({ { Operation::Delete, partFile } });
     } else {
         if (!QFile::remove(partFile)) {
             // Not a reason to fail the operation
             qCWarning(AKONADIPRIVATE_LOG) << "Error: failed to remove part file" << partFile;
         }
     }
 
     return true;
 }
 
 QByteArray ExternalPartStorage::updateFileNameRevision(const QByteArray &filename)
 {
     const int revIndex = filename.indexOf("_r");
     if (revIndex > -1) {
         QByteArray rev = filename.mid(revIndex + 2);
         int r = rev.toInt();
         r++;
         rev = QByteArray::number(r);
         return filename.left(revIndex + 2) + rev;
     }
 
     return filename + "_r0";
 }
 
 QByteArray ExternalPartStorage::nameForPartId(qint64 partId)
 {
     return QByteArray::number(partId) + "_r0";
 }
 
 bool ExternalPartStorage::beginTransaction()
 {
     QMutexLocker locker(&mTransactionLock);
     if (mTransactions.contains(QThread::currentThread())) {
         qCDebug(AKONADIPRIVATE_LOG) << "Error: there is already a transaction in progress in this thread";
         return false;
     }
 
     mTransactions.insert(QThread::currentThread(), QVector<Operation>());
     return true;
 }
 
 QString ExternalPartStorage::akonadiStoragePath()
 {
     return StandardDirs::saveDir("data", QStringLiteral("file_db_data"));
 }
 
 bool ExternalPartStorage::commitTransaction()
 {
     QMutexLocker locker(&mTransactionLock);
     auto iter = mTransactions.find(QThread::currentThread());
     if (iter == mTransactions.end()) {
         qCDebug(AKONADIPRIVATE_LOG) << "Commit error: there is no transaction in progress in this thread";
         return false;
     }
 
     const QVector<Operation> trx = iter.value();
     mTransactions.erase(iter);
     locker.unlock();
 
     return replayTransaction(trx, true);
 }
 
 bool ExternalPartStorage::rollbackTransaction()
 {
     QMutexLocker locker(&mTransactionLock);
     auto iter = mTransactions.find(QThread::currentThread());
     if (iter == mTransactions.end()) {
         qCDebug(AKONADIPRIVATE_LOG) << "Rollback error: there is no transaction in progress in this thread";
         return false;
     }
 
     const QVector<Operation> trx = iter.value();
     mTransactions.erase(iter);
     locker.unlock();
 
     return replayTransaction(trx, false);
 }
 
 bool ExternalPartStorage::inTransaction() const
 {
     QMutexLocker locker(&mTransactionLock);
     return mTransactions.contains(QThread::currentThread());
 }
 
 void ExternalPartStorage::addToTransaction(const QVector<Operation> &ops)
 {
     QMutexLocker locker(&mTransactionLock);
     auto iter = mTransactions.find(QThread::currentThread());
     Q_ASSERT(iter != mTransactions.end());
     locker.unlock();
 
     for (const Operation &op : ops) {
         iter->append(op);
     }
 }
 
 bool ExternalPartStorage::replayTransaction(const QVector<Operation> &trx, bool commit)
 {
     for (auto iter = trx.constBegin(), end = trx.constEnd(); iter != end; ++iter) {
         const Operation &op = *iter;
 
         if (op.type == Operation::Create) {
             if (commit) {
                 // no-op: we actually created that already in createPart()/updatePart()
             } else {
                 if (!QFile::remove(op.filename)) {
                     // We failed to remove the file, but don't abort the rollback.
                     // This is an error, but does not cause data loss.
                     qCDebug(AKONADIPRIVATE_LOG) << "Warning: failed to remove" << op.filename << "while rolling back a transaction";
                 }
             }
         } else if (op.type == Operation::Delete) {
             if (commit) {
                 if (!QFile::remove(op.filename)) {
                     // We failed to remove the file, but don't abort the commit.
                     // This is an error, but does not cause data loss.
                     qCDebug(AKONADIPRIVATE_LOG) << "Warning: failed to remove" << op.filename << "while committing a transaction";
                 }
             } else {
                 // no-op: we did not actually delete the file yet
             }
         } else {
             Q_UNREACHABLE();
         }
     }
 
     return true;
 }