diff --git a/src/calibre/ebooks/oeb/polish/container.py b/src/calibre/ebooks/oeb/polish/container.py
index d0795f6a67..bf585b4626 100644
--- a/src/calibre/ebooks/oeb/polish/container.py
+++ b/src/calibre/ebooks/oeb/polish/container.py
@@ -1195,7 +1195,7 @@ class EpubContainer(Container):
                     break
         if raw_unique_identifier is not None:
             idpf_key = raw_unique_identifier
-            idpf_key = re.sub(u'\u0020\u0009\u000d\u000a', u'', idpf_key)
+            idpf_key = re.sub(u'[\u0020\u0009\u000d\u000a]', u'', idpf_key)
             idpf_key = hashlib.sha1(idpf_key.encode('utf-8')).digest()
         key = None
         for item in self.opf_xpath('//*[local-name()="metadata"]/*'