diff --git a/Rakefile b/Rakefile
index f1ffc8ed..bf4785aa 100644
--- a/Rakefile
+++ b/Rakefile
@@ -52,6 +52,27 @@ file package('.tar.gz') => %w[dist/] + spec.files do |f|
   sh "git archive --format=tar HEAD | gzip > #{f.name}"
 end
 
+# Gemspec Helpers ====================================================
+
+file 'sinatra.gemspec' => FileList['{lib,test,images}/**','Rakefile'] do |f|
+  # read spec file and split out manifest section
+  spec = File.read(f.name)
+  parts = spec.split("  # = MANIFEST =\n")
+  fail 'bad spec' if parts.length != 3
+  # determine file list from git ls-files
+  files = `git ls-files`.
+    split("\n").
+    sort.
+    reject{ |file| file =~ /^\./ }.
+    map{ |file| "    #{file}" }.
+    join("\n")
+  # piece file back together and write...
+  parts[1] = "  s.files = %w[\n#{files}\n  ]\n"
+  spec = parts.join("  # = MANIFEST =\n")
+  File.open(f.name, 'w') { |io| io.write(spec) }
+  puts "updated #{f.name}"
+end
+
 # Hanna RDoc =========================================================
 #
 # Building docs requires the hanna gem:
diff --git a/sinatra.gemspec b/sinatra.gemspec
index 04699feb..cbd9c6ce 100644
--- a/sinatra.gemspec
+++ b/sinatra.gemspec
@@ -11,7 +11,7 @@ Gem::Specification.new do |s|
 
   s.authors = ["Blake Mizerany"]
 
-  # git ls-files | grep -v '^\.'
+  # = MANIFEST =
   s.files = %w[
     images/404.png
     images/500.png
@@ -58,6 +58,7 @@ Gem::Specification.new do |s|
     test/views/no_layout/no_layout.builder
     test/views/no_layout/no_layout.haml
   ]
+  # = MANIFEST =
 
   s.test_files = s.files.select {|path| path =~ /^test\/.*_test.rb/}