diff --git a/src/calibre/gui2/dialogs/metadata_single.py b/src/calibre/gui2/dialogs/metadata_single.py
index 10a81be9f5..d349298609 100644
--- a/src/calibre/gui2/dialogs/metadata_single.py
+++ b/src/calibre/gui2/dialogs/metadata_single.py
@@ -526,3 +526,11 @@ class MetadataSingleDialog(ResizableDialog, Ui_MetadataSingleDialog):
         QDialog.accept(self)
         if callable(self.accepted_callback):
             self.accepted_callback(self.id)
+
+    def reject(self, *args):
+        cf = getattr(self, 'cover_fetcher', None)
+        if cf is not None and hasattr(cf, 'terminate'):
+            cf.terminate()
+            cf.wait()
+
+        QDialog.reject(self, *args)