diff --git a/linkcheck/checker/urlbase.py b/linkcheck/checker/urlbase.py
index f152076b..fab6a427 100644
--- a/linkcheck/checker/urlbase.py
+++ b/linkcheck/checker/urlbase.py
@@ -329,6 +329,8 @@ class UrlBase (object):
             self.url = urljoin(self.parent_url, base_url, self.scheme)
         else:
             self.url = base_url
+        # note: urljoin can unnorm the url, so norm the url
+        self.url, is_idn = linkcheck.url.url_norm(self.url)
         # split into (modifiable) list
         self.urlparts = linkcheck.strformat.url_unicode_split(self.url)
         # and unsplit again