--- a/configmix/config.py	Sun Dec 19 16:04:40 2021 +0100
+++ b/configmix/config.py	Sun Dec 19 16:33:31 2021 +0100
@@ -690,14 +690,14 @@
         self.__cache[path] = v
         return v
 
-    def _lookupref(self, key, default=_MARKER):
+    def _lookupref(self, key):
         """
 
         `key` must be a configuration reference URI without any
         (namespace) prefixes and suffixes
 
         """
-        return self.expand_ref_uri(key, default=default)
+        return self.expand_ref_uri(key)
 
     def expand_if_reference(self, v):
         """Check whether `v` is a configuration reference and -- if true --
@@ -719,7 +719,7 @@
         else:
             return v
 
-    def expand_ref_uri(self, uri, default=_MARKER):
+    def expand_ref_uri(self, uri):
         pu = urlsplit(uri)
         if pu.scheme or pu.netloc or pu.path or pu.query:
             raise ValueError("only fragment-only URIs are supported")
@@ -727,7 +727,7 @@
             return self
         if pu.fragment.startswith(_DOT):
             raise ValueError("relative refs not supported")
-        return self.getvar(pu.fragment, default=default)
+        return self.getvar(pu.fragment)
 
     def substitute_variables_in_obj(self, obj):
         """Recursively expand variables in the object tree `obj`."""