x.diff

diff --git a/app/models/lookup_key.rb b/app/models/lookup_key.rb
index 256f07d..5c45396 100644
--- a/app/models/lookup_key.rb
+++ b/app/models/lookup_key.rb
@@ -150,8 +150,8 @@ class LookupKey < ActiveRecord::Base
     begin
       self.default_value = cast_validate_value self.default_value
       true
-    rescue
-      errors.add(:default_value, "is invalid")
+    rescue => e
+      errors.add(:default_value, "#{default_value}.inspect is invalid for #{to_s}: #{e}")
       false
     end
   end