diff --git a/serveradmin/serverdb/forms.py b/serveradmin/serverdb/forms.py
index e66264b2..31fc78e8 100644
--- a/serveradmin/serverdb/forms.py
+++ b/serveradmin/serverdb/forms.py
@@ -22,10 +22,11 @@ class Meta:
 
     def clean(self):
         # It makes no sense to add inet or supernet attributes to hosts of
-        # ip_addr_type null because they would have to be empty anyways.
+        # ip_addr_type null because they would have to be empty anyway.
         inet_attribute = (
+            'attribute' in self.cleaned_data and
             self.cleaned_data['attribute'].type in ('inet', 'supernet') and
-            self.instance.servertype.ip_addr_type == 'null'
+            self.cleaned_data['servertype'].ip_addr_type == 'null'
         )
         if inet_attribute:
             raise ValidationError(