diff --git a/src/calibre/ebooks/oeb/polish/check/parsing.py b/src/calibre/ebooks/oeb/polish/check/parsing.py
index 68427cb69d..2b28c0b7cc 100644
--- a/src/calibre/ebooks/oeb/polish/check/parsing.py
+++ b/src/calibre/ebooks/oeb/polish/check/parsing.py
@@ -209,8 +209,9 @@ def check_xml_parsing(name, mt, raw):
     except Exception as err:
         return errors + [errcls(err.message, name)]
 
-    if mt in OEB_DOCS and root.nsmap.get(root.prefix, None) != XHTML_NS:
-        errors.append(BadNamespace(name, root.nsmap.get(root.prefix, None)))
+    if mt in OEB_DOCS:
+        if root.nsmap.get(root.prefix, None) != XHTML_NS:
+            errors.append(BadNamespace(name, root.nsmap.get(root.prefix, None)))
 
     return errors