diff --git a/lib/jekyll/converters/markdown.rb b/lib/jekyll/converters/markdown.rb
index 485cac82..9727f5a4 100644
--- a/lib/jekyll/converters/markdown.rb
+++ b/lib/jekyll/converters/markdown.rb
@@ -8,20 +8,22 @@ module Jekyll
 
       def setup
         return if @setup
-        @parser = case @config['markdown']
-          when 'redcarpet'
-            RedcarpetParser.new @config
-          when 'kramdown'
-            KramdownParser.new @config
-          when 'rdiscount'
-            RDiscountParser.new @config
-          when 'maruku'
-            MarukuParser.new @config
+        @parser =
+          case @config['markdown']
+            when 'redcarpet' then RedcarpetParser.new(@config)
+            when 'kramdown' then KramdownParser.new(@config)
+            when 'rdiscount' then RDiscountParser.new(@config)
+            when 'maruku' then MarukuParser.new(@config)
           else
-            STDERR.puts "Invalid Markdown processor: #{@config['markdown']}"
-            STDERR.puts "  Valid options are [ maruku | rdiscount | kramdown | redcarpet ]"
-            raise FatalException.new("Invalid Markdown process: #{@config['markdown']}")
-        end
+            # So they can't try some tricky bullshit or go down the ancestor chain, I hope.
+            if @config['markdown'] !~ /[^A-Za-z0-9]/ && self.class.constants.include?(@config['markdown'].to_sym)
+              self.class.const_get(@config['markdown']).new(@config)
+            else
+              Jekyll.logger.error "Invalid Markdown Processor:", "#{@config['markdown']}"
+              Jekyll.logger.error "", "Valid options are [ maruku | rdiscount | kramdown | redcarpet ]"
+              raise FatalException, "Invalid Markdown process: #{@config['markdown']}"
+            end
+          end
         @setup = true
       end
 
diff --git a/test/test_site.rb b/test/test_site.rb
index a530f9d0..04e2b3d0 100644
--- a/test/test_site.rb
+++ b/test/test_site.rb
@@ -262,6 +262,52 @@ class TestSite < Test::Unit::TestCase
       end
     end
 
+    context 'using a non-default markdown processor in the configuration' do
+      should 'use the non-default markdown processor' do
+        class Jekyll::Converters::Markdown::CustomMarkdown
+          def initialize(*args)
+            @args = args
+          end
+
+          def convert(*args)
+            ""
+          end
+        end
+
+        custom_processor = "CustomMarkdown"
+        s = Site.new(Jekyll.configuration.merge({ 'markdown' => custom_processor }))
+        assert_nothing_raised do
+          s.process
+        end
+
+        # Do some cleanup, we don't like straggling stuff's.
+        Jekyll::Converters::Markdown.send(:remove_const, :CustomMarkdown)
+      end
+
+      should 'ignore, if there are any bad characters in the class name' do
+        module Jekyll::Converters::Markdown::Custom
+          class Markdown
+            def initialize(*args)
+              @args = args
+            end
+
+            def convert(*args)
+              ""
+            end
+          end
+        end
+
+        bad_processor = "Custom::Markdown"
+        s = Site.new(Jekyll.configuration.merge({ 'markdown' => bad_processor }))
+        assert_raise Jekyll::FatalException do
+          s.process
+        end
+
+        # Do some cleanup, we don't like straggling stuff's.
+        Jekyll::Converters::Markdown.send(:remove_const, :Custom)
+      end
+    end
+
     context 'with an invalid markdown processor in the configuration' do
       should 'not throw an error at initialization time' do
         bad_processor = 'not a processor name'