diff --git a/src/oidcmsg/__init__.py b/src/oidcmsg/__init__.py
index 388b6ff..ef1bd14 100644
--- a/src/oidcmsg/__init__.py
+++ b/src/oidcmsg/__init__.py
@@ -1,5 +1,5 @@
 __author__ = "Roland Hedberg"
-__version__ = "1.5.4"
+__version__ = "1.6.0"
 
 import os
 from typing import Dict
diff --git a/src/oidcmsg/configure.py b/src/oidcmsg/configure.py
index 26f65cb..d9b0c4b 100644
--- a/src/oidcmsg/configure.py
+++ b/src/oidcmsg/configure.py
@@ -105,12 +105,12 @@ def __getattr__(self, item, default=None):
             return default
 
     def __setattr__(self, key, value):
-        if key in self:
+        if key in self and self.key:
             raise KeyError('{} has already been set'.format(key))
         super(Base, self).__setitem__(key, value)
 
     def __setitem__(self, key, value):
-        if key in self:
+        if key in self and self.key:
             raise KeyError('{} has already been set'.format(key))
         super(Base, self).__setitem__(key, value)