diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 25b6d1aaae..9bab688ba5 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -707,7 +707,7 @@ OptionRecommendation(name='timestamp',
             if mi.cover.startswith('http:') or mi.cover.startswith('https:'):
                 mi.cover = self.download_cover(mi.cover)
             ext = mi.cover.rpartition('.')[-1].lower().strip()
-            if ext not in ('png', 'jpg', 'jpeg'):
+            if ext not in ('png', 'jpg', 'jpeg', 'gif'):
                 ext = 'jpg'
             mi.cover_data = (ext, open(mi.cover, 'rb').read())
             mi.cover = None
diff --git a/src/calibre/gui2/convert/metadata.py b/src/calibre/gui2/convert/metadata.py
index ea62b61f6a..1645cec400 100644
--- a/src/calibre/gui2/convert/metadata.py
+++ b/src/calibre/gui2/convert/metadata.py
@@ -21,6 +21,7 @@ from calibre.gui2.convert import Widget
 def create_opf_file(db, book_id):
     mi = db.get_metadata(book_id, index_is_id=True)
     mi.application_id = uuid.uuid4()
+    mi.cover = None
     raw = metadata_to_opf(mi)
     opf_file = PersistentTemporaryFile('.opf')
     opf_file.write(raw)