diff --git a/src/calibre/db/cli/cmd_add.py b/src/calibre/db/cli/cmd_add.py
index c487ddc48f..ac302da475 100644
--- a/src/calibre/db/cli/cmd_add.py
+++ b/src/calibre/db/cli/cmd_add.py
@@ -15,7 +15,7 @@ from calibre.db.adding import (
     run_import_plugins, run_import_plugins_before_metadata
 )
 from calibre.ebooks.metadata import MetaInformation, string_to_authors
-from calibre.ebooks.metadata.book.serialize import read_cover
+from calibre.ebooks.metadata.book.serialize import read_cover, serialize_cover
 from calibre.ebooks.metadata.meta import get_metadata, metadata_from_formats
 from calibre.ptempfile import TemporaryDirectory
 from calibre.srv.changes import books_added
@@ -160,7 +160,7 @@ def do_add(
                 continue
             ids, dups, book_title = dbctx.run(
                 'add', 'book', dbctx.path(book), os.path.basename(book), fmt, add_duplicates,
-                otitle, oauthors, oisbn, otags, oseries, oseries_index, read_cover(ocover) if ocover else None,
+                otitle, oauthors, oisbn, otags, oseries, oseries_index, serialize_cover(ocover) if ocover else None,
                 oidentifiers, olanguages
             )
             added_ids |= set(ids)
diff --git a/src/calibre/ebooks/metadata/book/serialize.py b/src/calibre/ebooks/metadata/book/serialize.py
index 06e458ad5b..fdca2d0610 100644
--- a/src/calibre/ebooks/metadata/book/serialize.py
+++ b/src/calibre/ebooks/metadata/book/serialize.py
@@ -24,14 +24,18 @@ def ensure_unicode(obj, enc=preferred_encoding):
     return obj
 
 
+def serialize_cover(path):
+    with lopen(path, 'rb') as f:
+        cd = f.read()
+    return what(None, cd), cd
+
+
 def read_cover(mi):
     if mi.cover_data and mi.cover_data[1]:
         return mi
     if mi.cover:
         try:
-            with lopen(mi.cover, 'rb') as f:
-                cd = f.read()
-            mi.cover_data = what(None, cd), cd
+            mi.cover_data = serialize_cover(mi.cover)
         except EnvironmentError:
             pass
     return mi