diff --git a/src/calibre/ebooks/oeb/polish/check/opf.py b/src/calibre/ebooks/oeb/polish/check/opf.py
index 76f8418b4e..e2f6abd0e3 100644
--- a/src/calibre/ebooks/oeb/polish/check/opf.py
+++ b/src/calibre/ebooks/oeb/polish/check/opf.py
@@ -370,7 +370,7 @@ def check_opf(container):
                 errors.append(IncorrectCover(container.opf_name, cover.sourceline, cover.get('content', '')))
             raw = etree.tostring(cover)
             try:
-                n, c = raw.index('name="'), raw.index('content="')
+                n, c = raw.index(b'name="'), raw.index(b'content="')
             except ValueError:
                 n = c = -1
             if n > -1 and c > -1 and n > c:
diff --git a/src/calibre/ebooks/oeb/polish/cover.py b/src/calibre/ebooks/oeb/polish/cover.py
index 941ef71d17..b84a938a94 100644
--- a/src/calibre/ebooks/oeb/polish/cover.py
+++ b/src/calibre/ebooks/oeb/polish/cover.py
@@ -393,8 +393,10 @@ def create_epub_cover(container, cover_path, existing_image, options=None):
     titlepage_item = container.generate_item(tname, id_prefix='titlepage')
     titlepage = container.href_to_name(titlepage_item.get('href'),
                                           container.opf_name)
-    raw = templ%container.name_to_href(raster_cover, titlepage).encode('utf-8')
+    raw = templ % container.name_to_href(raster_cover, titlepage)
     with container.open(titlepage, 'wb') as f:
+        if not isinstance(raw, bytes):
+            raw = raw.encode('utf-8')
         f.write(raw)
 
     # We have to make sure the raster cover item has id="cover" for the moron