diff --git a/src/calibre/gui2/dialogs/metadata_bulk.py b/src/calibre/gui2/dialogs/metadata_bulk.py
index f0baaaf17a..5f6d3bcc3a 100644
--- a/src/calibre/gui2/dialogs/metadata_bulk.py
+++ b/src/calibre/gui2/dialogs/metadata_bulk.py
@@ -212,7 +212,7 @@ class MyBlockingBusyNew(QDialog):  # {{{
                     im = Image()
                     im.load(cdata)
                     im.trim(tweaks['cover_trim_fuzz_value'])
-                    cdata = im.export('png')
+                    cdata = im.export('jpg')
                     cache.set_cover({book_id:cdata})
 
         # Formats
@@ -440,7 +440,7 @@ class MyBlockingBusy(QDialog):  # {{{
                     im = Image()
                     im.load(cdata)
                     im.trim(tweaks['cover_trim_fuzz_value'])
-                    cdata = im.export('png')
+                    cdata = im.export('jpg')
                     self.db.set_cover(id, cdata)
 
             if do_remove_format:
diff --git a/src/calibre/gui2/metadata/basic_widgets.py b/src/calibre/gui2/metadata/basic_widgets.py
index a675220117..0fb2d0b197 100644
--- a/src/calibre/gui2/metadata/basic_widgets.py
+++ b/src/calibre/gui2/metadata/basic_widgets.py
@@ -972,7 +972,7 @@ class Cover(ImageView):  # {{{
         im = Image()
         im.load(cdata)
         im.trim(tweaks['cover_trim_fuzz_value'])
-        cdata = im.export('png')
+        cdata = im.export('jpg')
         self.current_val = cdata
 
     def generate_cover(self, *args):