diff --git a/src/calibre/ebooks/oeb/polish/container.py b/src/calibre/ebooks/oeb/polish/container.py
index 4dc6f0ea4b..972bedbee7 100644
--- a/src/calibre/ebooks/oeb/polish/container.py
+++ b/src/calibre/ebooks/oeb/polish/container.py
@@ -1006,7 +1006,7 @@ class Container(ContainerBase):  # {{{
         if name == self.opf_name and root.nsmap.get(None) == OPF2_NS:
             # Needed as I can't get lxml to output opf:role and
             # not output <opf:metadata> as well
-            data = re.sub(br'(<[/]{0,1})opf:', r'\1', data)
+            data = re.sub(br'(<[/]{0,1})opf:', br'\1', data)
         return data
 
     def commit_item(self, name, keep_parsed=False):