diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py index 1f87dcbe45..e330668a34 100644 --- a/src/calibre/ebooks/oeb/base.py +++ b/src/calibre/ebooks/oeb/base.py @@ -702,7 +702,7 @@ class Metadata(object): term = CALIBRE(local) self.term = term self.value = value - for attr, value in attrib.items(): + for attr, value in tuple(iteritems(attrib)): if isprefixname(value): attrib[attr] = qname(value, nsmap) nsattr = Metadata.OPF_ATTRS.get(attr, attr)