diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index f690155f2e84c35b1a60c3ba810465021da2665e..cb94fa38a510825a2f6277651f9c87df9cc9c1b9 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -592,7 +592,7 @@ class GitDownloadStrategy < VCSDownloadStrategy
   end
 
   def last_commit
-    Utils.popen_read("git", "--git-dir", git_dir ,"rev-parse", "HEAD").chomp
+    Utils.popen_read("git", "--git-dir", git_dir ,"rev-parse", "--short", "HEAD").chomp
   end
 
   private