diff --git a/lib/jekyll/post.rb b/lib/jekyll/post.rb
index 914cfd59..a86f31a2 100644
--- a/lib/jekyll/post.rb
+++ b/lib/jekyll/post.rb
@@ -47,26 +47,10 @@ module Jekyll
         self.published = true
       end
 
-      if self.data.has_key?("tag")
-        self.tags = [self.data["tag"]]
-      elsif self.data.has_key?("tags")
-        self.tags = self.data['tags']
-      else
-        self.tags = []
-      end
+      self.tags = self.data.pluralized_array("tag", "tags")
 
       if self.categories.empty?
-        if self.data.has_key?('category')
-          self.categories << self.data['category']
-        elsif self.data.has_key?('categories')
-          # Look for categories in the YAML-header, either specified as
-          # an array or a string.
-          if self.data['categories'].kind_of? String
-            self.categories = self.data['categories'].split
-          else
-            self.categories = self.data['categories']
-          end
-        end
+        self.categories = self.data.pluralized_array('category', 'categories')
       end
     end