diff --git a/kindlecomicconverter/KCC_gui.py b/kindlecomicconverter/KCC_gui.py
index 0990fcb..c8a6ecc 100644
--- a/kindlecomicconverter/KCC_gui.py
+++ b/kindlecomicconverter/KCC_gui.py
@@ -16,6 +16,8 @@
 # OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 # TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 # PERFORMANCE OF THIS SOFTWARE.
+
+import itertools
 from pathlib import Path
 from PySide6.QtCore import (QSize, QUrl, Qt, Signal, QIODeviceBase, QEvent, QThread, QSettings)
 from PySide6.QtGui import (QColor, QIcon, QPixmap, QDesktopServices)
@@ -490,13 +492,24 @@ class SystemTrayIcon(QSystemTrayIcon):
 class KCCGUI(KCC_ui.Ui_mainWindow):
     def selectDefaultOutputFolder(self):
         dname = QFileDialog.getExistingDirectory(MW, 'Select default output folder', self.defaultOutputFolder)
+        if self.is_directory_on_kindle(dname):
+            return
         if dname != '':
             if sys.platform.startswith('win'):
                 dname = dname.replace('/', '\\')
             GUI.defaultOutputFolder = dname
 
+    def is_directory_on_kindle(self, dname):
+        path = Path(dname)
+        for parent in itertools.chain([path], path.parents):
+            if parent.name == 'documents' and parent.parent.joinpath('system').joinpath('thumbnails').is_dir():
+                self.addMessage("Cannot select Kindle as output directory", 'error')
+                return True
+
     def selectOutputFolder(self):
         dname = QFileDialog.getExistingDirectory(MW, 'Select output directory', self.lastPath)
+        if self.is_directory_on_kindle(dname):
+            return
         if dname != '':
             if sys.platform.startswith('win'):
                 dname = dname.replace('/', '\\')