diff --git a/src/calibre/ebooks/oeb/transforms/cover.py b/src/calibre/ebooks/oeb/transforms/cover.py
index 4d41ab14b4..83c5ec93e4 100644
--- a/src/calibre/ebooks/oeb/transforms/cover.py
+++ b/src/calibre/ebooks/oeb/transforms/cover.py
@@ -103,8 +103,8 @@ class CoverManager(object):
                 32)]
             img_data = create_cover_page(lines, I('library.png'))
             id, href = self.oeb.manifest.generate('cover_image',
-                    'cover_image.png')
-            item = self.oeb.manifest.add(id, href, guess_type('t.png')[0],
+                    'cover_image.jpg')
+            item = self.oeb.manifest.add(id, href, guess_type('t.jpg')[0],
                         data=img_data)
             m.clear('cover')
             m.add('cover', item.id)
diff --git a/src/calibre/utils/magick_draw.py b/src/calibre/utils/magick_draw.py
index 160f4b70a5..2a259301db 100644
--- a/src/calibre/utils/magick_draw.py
+++ b/src/calibre/utils/magick_draw.py
@@ -175,7 +175,7 @@ def add_borders_to_image(path_to_image, left=0, top=0, right=0, bottom=0,
         p.DestroyMagickWand(canvas)
 
 def create_cover_page(top_lines, logo_path, width=590, height=750,
-        bgcolor='white', output_format='png'):
+        bgcolor='white', output_format='jpg'):
     ans = None
     with p.ImageMagick():
         canvas = create_canvas(width, height, bgcolor)