diff --git a/src/calibre/ebooks/conversion/plugins/epub_input.py b/src/calibre/ebooks/conversion/plugins/epub_input.py
index af7a5e2380..20a8b3ac26 100644
--- a/src/calibre/ebooks/conversion/plugins/epub_input.py
+++ b/src/calibre/ebooks/conversion/plugins/epub_input.py
@@ -39,7 +39,7 @@ class EPUBInput(InputFormatPlugin):
         import uuid, hashlib
         idpf_key = opf.raw_unique_identifier
         if idpf_key:
-            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 opf.identifier_iter():