diff --git a/lib/jekyll/convertible.rb b/lib/jekyll/convertible.rb
index 863fa4eb..35f6b0f4 100644
--- a/lib/jekyll/convertible.rb
+++ b/lib/jekyll/convertible.rb
@@ -146,7 +146,7 @@ module Jekyll
     #
     # Returns true if extname == .sass or .scss, false otherwise.
     def sass_file?
-      %w(.sass .scss).include?(ext)
+      Jekyll::Document::SASS_FILE_EXTS.include?(ext)
     end
 
     # Determine whether the document is a CoffeeScript file.
diff --git a/lib/jekyll/document.rb b/lib/jekyll/document.rb
index a8fda1e8..7e9e42ca 100644
--- a/lib/jekyll/document.rb
+++ b/lib/jekyll/document.rb
@@ -14,6 +14,9 @@ module Jekyll
     DATELESS_FILENAME_MATCHER = %r!^(?:.+/)*(.*)(\.[^.]+)$!.freeze
     DATE_FILENAME_MATCHER = %r!^(?>.+/)*?(\d{2,4}-\d{1,2}-\d{1,2})-([^/]*)(\.[^.]+)$!.freeze
 
+    SASS_FILE_EXTS = %w(.sass .scss).freeze
+    YAML_FILE_EXTS = %w(.yaml .yml).freeze
+
     # Create a new Document.
     #
     # path - the path to the file
@@ -138,7 +141,7 @@ module Jekyll
     #
     # Returns true if the extname is either .yml or .yaml, false otherwise.
     def yaml_file?
-      %w(.yaml .yml).include?(extname)
+      YAML_FILE_EXTS.include?(extname)
     end
 
     # Determine whether the document is an asset file.
@@ -154,7 +157,7 @@ module Jekyll
     #
     # Returns true if extname == .sass or .scss, false otherwise.
     def sass_file?
-      %w(.sass .scss).include?(extname)
+      SASS_FILE_EXTS.include?(extname)
     end
 
     # Determine whether the document is a CoffeeScript file.