diff --git a/lib/jekyll/converters/markdown.rb b/lib/jekyll/converters/markdown.rb
index 687b0eca..da37d249 100644
--- a/lib/jekyll/converters/markdown.rb
+++ b/lib/jekyll/converters/markdown.rb
@@ -8,6 +8,7 @@ module Jekyll
 
       def setup
         return if @setup
+        @regexp = build_extname_regexp
         @parser =
           case @config['markdown'].downcase
             when 'redcarpet' then RedcarpetParser.new(@config)
@@ -27,6 +28,11 @@ module Jekyll
         @setup = true
       end
 
+      def build_extname_regexp
+        rgx = '^\.(' + @config['markdown_ext'].gsub(',','|') +')$'
+        Regexp.new(rgx, Regexp::IGNORECASE)
+      end
+
       def valid_processors
         %w[
           maruku
@@ -47,8 +53,7 @@ module Jekyll
       end
 
       def matches(ext)
-        rgx = '^\.(' + @config['markdown_ext'].gsub(',','|') +')$'
-        ext =~ Regexp.new(rgx, Regexp::IGNORECASE)
+        ext =~ @regexp
       end
 
       def output_ext(ext)
diff --git a/lib/jekyll/converters/textile.rb b/lib/jekyll/converters/textile.rb
index 366aa0ce..8c366908 100644
--- a/lib/jekyll/converters/textile.rb
+++ b/lib/jekyll/converters/textile.rb
@@ -9,6 +9,7 @@ module Jekyll
       def setup
         return if @setup
         require 'redcloth'
+        @regexp = build_extname_regexp
         @setup = true
       rescue LoadError
         STDERR.puts 'You are missing a library required for Textile. Please run:'
@@ -16,9 +17,13 @@ module Jekyll
         raise Errors::FatalException.new("Missing dependency: RedCloth")
       end
 
+      def build_extname_regexp
+        rgx = '(' + @config['textile_ext'].gsub(',','|') +')$'
+        Regexp.new(rgx, Regexp::IGNORECASE)
+      end
+
       def matches(ext)
-        rgx = '(' + @config['textile_ext'].gsub(',','|') +')'
-        ext =~ Regexp.new(rgx, Regexp::IGNORECASE)
+        ext =~ @regexp
       end
 
       def output_ext(ext)