diff --git a/lib/jekyll/filters.rb b/lib/jekyll/filters.rb
index 3ee63188..002d926f 100644
--- a/lib/jekyll/filters.rb
+++ b/lib/jekyll/filters.rb
@@ -207,9 +207,8 @@ module Jekyll
         when nils == "last"
           order = + 1
         else
-          Jekyll.logger.error "Invalid nils order:",
-            "'#{nils}' is not a valid nils order. It must be 'first' or 'last'."
-          exit(1)
+          raise ArgumentError.new("Invalid nils order: " +
+            "'#{nils}' is not a valid nils order. It must be 'first' or 'last'.")
         end
 
         input.sort { |apple, orange|
@@ -247,7 +246,9 @@ module Jekyll
     end
 
     def item_property(item, property)
-      if item.respond_to?(:data)
+      if item.respond_to?(:to_liquid)
+        item.to_liquid[property.to_s]
+      elsif item.respond_to?(:data)
         item.data[property.to_s]
       else
         item[property.to_s]