diff --git a/lib/thumbnailprovider/thumbnailgenerator.h b/lib/thumbnailprovider/thumbnailgenerator.h
--- a/lib/thumbnailprovider/thumbnailgenerator.h
+++ b/lib/thumbnailprovider/thumbnailgenerator.h
@@ -51,6 +51,10 @@
 public:
     ThumbnailGenerator();
 
+    // Because we override run(), like you're not really supposed to do, we
+    // can't trust isRunning()
+    bool isStopped();
+
     void load(
         const QString& originalUri,
         time_t originalTime,
@@ -89,6 +93,7 @@
     QWaitCondition mCond;
     ThumbnailGroup::Enum mThumbnailGroup;
     bool mCancel;
+    bool mStopped = false;
 };
 
 } // namespace
diff --git a/lib/thumbnailprovider/thumbnailgenerator.cpp b/lib/thumbnailprovider/thumbnailgenerator.cpp
--- a/lib/thumbnailprovider/thumbnailgenerator.cpp
+++ b/lib/thumbnailprovider/thumbnailgenerator.cpp
@@ -36,6 +36,7 @@
 #include <QImageReader>
 #include <QTransform>
 #include <QBuffer>
+#include <QCoreApplication>
 
 namespace Gwenview
 {
@@ -178,7 +179,12 @@
 //------------------------------------------------------------------------
 ThumbnailGenerator::ThumbnailGenerator()
 : mCancel(false)
-{}
+{
+    connect(qApp, &QCoreApplication::aboutToQuit, this, [=]() {
+        wait();
+    }, Qt::DirectConnection);
+    start();
+}
 
 void ThumbnailGenerator::load(
     const QString& originalUri, time_t originalTime, KIO::filesize_t originalFileSize, const QString& originalMimeType,
@@ -196,15 +202,20 @@
     mPixPath = pixPath;
     mThumbnailPath = thumbnailPath;
     mThumbnailGroup = group;
-    if (!isRunning()) start();
     mCond.wakeOne();
 }
 
 QString ThumbnailGenerator::originalUri() const
 {
     return mOriginalUri;
 }
 
+bool ThumbnailGenerator::isStopped()
+{
+    QMutexLocker lock(&mMutex);
+    return mStopped;
+}
+
 time_t ThumbnailGenerator::originalTime() const
 {
     return mOriginalTime;
@@ -235,21 +246,18 @@
 
 void ThumbnailGenerator::run()
 {
-    LOG("");
     while (!testCancel()) {
         QString pixPath;
         int pixelSize;
         {
             QMutexLocker lock(&mMutex);
             // empty mPixPath means nothing to do
-            LOG("Waiting for mPixPath");
             if (mPixPath.isNull()) {
-                LOG("mPixPath.isNull");
                 mCond.wait(&mMutex);
             }
         }
         if (testCancel()) {
-            return;
+            break;
         }
         {
             QMutexLocker lock(&mMutex);
@@ -279,7 +287,7 @@
             mPixPath.clear(); // done, ready for next
         }
         if (testCancel()) {
-            return;
+            break;
         }
         {
             QSize size(mOriginalWidth, mOriginalHeight);
@@ -289,7 +297,12 @@
             LOG("Done");
         }
     }
+
     LOG("Ending thread");
+
+    QMutexLocker lock(&mMutex);
+    mStopped = true;
+    deleteLater();
 }
 
 void ThumbnailGenerator::cacheThumbnail()
diff --git a/lib/thumbnailprovider/thumbnailprovider.cpp b/lib/thumbnailprovider/thumbnailprovider.cpp
--- a/lib/thumbnailprovider/thumbnailprovider.cpp
+++ b/lib/thumbnailprovider/thumbnailprovider.cpp
@@ -175,11 +175,10 @@
 ThumbnailProvider::~ThumbnailProvider()
 {
     LOG(this);
-    abortSubjob();
-    mThumbnailGenerator->cancel();
     disconnect(mThumbnailGenerator, nullptr, this, nullptr);
     disconnect(mThumbnailGenerator, nullptr, sThumbnailWriter, nullptr);
-    connect(mThumbnailGenerator, SIGNAL(finished()), mThumbnailGenerator, SLOT(deleteLater()));
+    abortSubjob();
+    mThumbnailGenerator->cancel();
     if (mPreviousThumbnailGenerator) {
         disconnect(mPreviousThumbnailGenerator, nullptr, sThumbnailWriter, nullptr);
     }
@@ -193,7 +192,7 @@
     // startCreatingThumbnail() will take care that these two threads won't work on the same item.
     mItems.clear();
     abortSubjob();
-    if (mThumbnailGenerator->isRunning() && !mPreviousThumbnailGenerator) {
+    if (!mThumbnailGenerator->isStopped() && !mPreviousThumbnailGenerator) {
         mPreviousThumbnailGenerator = mThumbnailGenerator;
         mPreviousThumbnailGenerator->cancel();
         disconnect(mPreviousThumbnailGenerator, nullptr, this, nullptr);
@@ -524,7 +523,7 @@
     // connect mPreviousThumbnailGenerator's signal "finished" to determineNextIcon
     // which will load the thumbnail from sThumbnailWriter or from disk
     // (because we re-add mCurrentItem to mItems).
-    if (mPreviousThumbnailGenerator && mPreviousThumbnailGenerator->isRunning() &&
+    if (mPreviousThumbnailGenerator && !mPreviousThumbnailGenerator->isStopped() &&
         mOriginalUri == mPreviousThumbnailGenerator->originalUri() &&
         mOriginalTime == mPreviousThumbnailGenerator->originalTime() &&
         mOriginalFileSize == mPreviousThumbnailGenerator->originalFileSize() &&