--- a/pvl/hosts/config.py	Tue Feb 24 19:18:45 2015 +0200
+++ b/pvl/hosts/config.py	Tue Feb 24 19:24:06 2015 +0200
@@ -123,10 +123,13 @@
         else:
             f = fields
         
-        if instance:
+        if not instance and field not in f:
+            f[field] = value
+
+        elif field not in f:
+            f[field] = {instance: value}
+        elif isinstance(f[field], dict):
             f.setdefault(field, {})[instance] = value
-        elif field not in f:
-            f[field] = value
         else:
             raise HostConfigError(None, "{name}: override instanced {field} value: {value}".format(name=name, field=field, value=value))