diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index a9827d9150..3b38536e4f 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -693,9 +693,8 @@ class Metadata(object):
     def to_opf2(self, parent=None):
         nsmap = self._opf2_nsmap
         nsrmap = dict((value, key) for key, value in nsmap.items())
-        nmap = dict(**nsmap)
-        nmap.pop('opf', '')
-        elem = element(parent, OPF('metadata'), nsmap=nmap)
+        nsmap.pop('opf', '')
+        elem = element(parent, OPF('metadata'), nsmap=nsmap)
         for term in self.items:
             for item in self.items[term]:
                 item.to_opf2(elem, nsrmap=nsrmap)