diff --git a/src/calibre/ebooks/oeb/iterator/book.py b/src/calibre/ebooks/oeb/iterator/book.py
index 4ebd543aab..d3cedce688 100644
--- a/src/calibre/ebooks/oeb/iterator/book.py
+++ b/src/calibre/ebooks/oeb/iterator/book.py
@@ -143,7 +143,7 @@ class EbookIterator(BookmarksMixin):
 
         cover = self.opf.cover
         if cover and self.ebook_ext in {'lit', 'mobi', 'prc', 'opf', 'fb2',
-                                        'azw', 'azw3'}:
+                                        'azw', 'azw3', 'docx'}:
             cfile = os.path.join(self.base, 'calibre_iterator_cover.html')
             rcpath = os.path.relpath(cover, self.base).replace(os.sep, '/')
             chtml = (TITLEPAGE%prepare_string_for_xml(rcpath, True)).encode('utf-8')