diff --git a/lib/jekyll/configuration.rb b/lib/jekyll/configuration.rb
index 0c68365a..20bbbb67 100644
--- a/lib/jekyll/configuration.rb
+++ b/lib/jekyll/configuration.rb
@@ -123,7 +123,10 @@ module Jekyll
       # Get configuration from <source>/_config.yml or <source>/<config_file>
       config_files = override.delete('config')
       if config_files.to_s.empty?
-        config_files = File.join(source(override), "_config.yml")
+        default = %w[yml yaml].find(Proc.new { 'yml' }) do |ext|
+          File.exists? Jekyll.sanitized_path(source(override), "_config.#{ext}")
+        end
+        config_files = Jekyll.sanitized_path(source(override), "_config.#{default}")
         @default_config_file = true
       end
       config_files = [config_files] unless config_files.is_a? Array
diff --git a/test/test_configuration.rb b/test/test_configuration.rb
index bfb37adf..bdb4dc83 100644
--- a/test/test_configuration.rb
+++ b/test/test_configuration.rb
@@ -39,7 +39,16 @@ class TestConfiguration < Test::Unit::TestCase
       assert @config.config_files(@multiple_files).is_a?(Array)
     end
     should "return the default config path if no config files are specified" do
-      assert_equal [File.join(source_dir, "_config.yml")], @config.config_files(@no_override)
+      assert_equal [source_dir("_config.yml")], @config.config_files(@no_override)
+    end
+    should "return .yaml if it exists but .yml does not" do
+      mock(File).exists?(source_dir("_config.yml")) { false }
+      mock(File).exists?(source_dir("_config.yaml")) { true }
+      assert_equal [source_dir("_config.yaml")], @config.config_files(@no_override)
+    end
+    should "return .yml if both .yml and .yaml exist" do
+      mock(File).exists?(source_dir("_config.yml")) { true }
+      assert_equal [source_dir("_config.yml")], @config.config_files(@no_override)
     end
     should "return the config if given one config file" do
       assert_equal %w[config.yml], @config.config_files(@one_config_file)