diff --git a/devpi_ldap/main.py b/devpi_ldap/main.py
index ecfc72e..e0a2d96 100644
--- a/devpi_ldap/main.py
+++ b/devpi_ldap/main.py
@@ -180,7 +180,10 @@ def extract_search(s):
                         return []
             elif attribute_name in ('dn', 'distinguishedName'):
                 def extract_search(s):
-                    return [s[attribute_name]]
+                    if attribute_name in s:
+                        return [s[attribute_name]]
+                    else:
+                        return []
             else:
                 threadlog.error('configured attribute_name {} not found in any search results'.format(attribute_name))
                 return []