diff --git a/bin/linguist b/bin/linguist
index 2cfa8064..e086dcea 100755
--- a/bin/linguist
+++ b/bin/linguist
@@ -5,6 +5,7 @@
 
 require 'linguist/file_blob'
 require 'linguist/repository'
+require 'rugged'
 
 path = ARGV[0] || Dir.pwd
 
@@ -18,7 +19,8 @@ ARGV.shift
 breakdown = true if ARGV[0] == "--breakdown"
 
 if File.directory?(path)
-  repo = Linguist::Repository.from_directory(path)
+  rugged = Rugged::Repository.new(path)
+  repo = Linguist::Repository.new(rugged, rugged.head.target_id)
   repo.languages.sort_by { |_, size| size }.reverse.each do |language, size|
     percentage = ((size / repo.size.to_f) * 100)
     percentage = sprintf '%.2f' % percentage
diff --git a/lib/linguist/repository.rb b/lib/linguist/repository.rb
index 82e9ef47..e3d2d707 100644
--- a/lib/linguist/repository.rb
+++ b/lib/linguist/repository.rb
@@ -29,6 +29,8 @@ module Linguist
     def initialize(repo, commit_oid)
       @repository = repo
       @commit_oid = commit_oid
+
+      raise TypeError, 'commit_oid must be a commit SHA1' unless commit_oid.is_a?(String)
     end
 
     # Public: Load the results of a previous analysis on this repository