diff --git a/src/calibre/gui2/dialogs/choose_format.py b/src/calibre/gui2/dialogs/choose_format.py
index c9ef37118b..f8c3d54d1f 100644
--- a/src/calibre/gui2/dialogs/choose_format.py
+++ b/src/calibre/gui2/dialogs/choose_format.py
@@ -41,6 +41,7 @@ class ChooseFormatDialog(QDialog):
         bb.accepted.connect(self.accept), bb.rejected.connect(self.reject)
         h.addStretch(10), h.addWidget(self.buttonBox)
 
+        formats = list(formats)
         for format in formats:
             self.formats.addItem(QListWidgetItem(file_icon_provider().icon_from_ext(format.lower()),
                                                  format.upper()))
diff --git a/src/calibre/gui2/store/search/search.py b/src/calibre/gui2/store/search/search.py
index b4a09d610a..09eb34c472 100644
--- a/src/calibre/gui2/store/search/search.py
+++ b/src/calibre/gui2/store/search/search.py
@@ -392,7 +392,7 @@ class SearchDialog(QDialog, Ui_Dialog):
             self.open_store(result)
 
     def download_book(self, result):
-        d = ChooseFormatDialog(self, _('Choose format to download to your library.'), result.downloads.keys())
+        d = ChooseFormatDialog(self, _('Choose format to download to your library.'), list(result.downloads.keys()))
         if d.exec_() == d.Accepted:
             ext = d.format()
             fname = result.title[:60] + '.' + ext.lower()