diff --git a/lib/ldapter/attribute_set.rb b/lib/ldapter/attribute_set.rb
index <HASH>..<HASH> 100644
--- a/lib/ldapter/attribute_set.rb
+++ b/lib/ldapter/attribute_set.rb
@@ -81,7 +81,9 @@ module Ldapter
       elsif mandatory? && @target.empty?
         errors << "is mandatory"
       end
-      errors += @target.map { |v| syntax_object.error(v) }.compact
+      if syntax_object
+        errors += @target.map { |v| syntax_object.error(v) }.compact
+      end
       errors
     end
Don't blow up on validating missing syntax object