raise when Rubygems version doesn't exist

1 files changed, 1 insertions, 1 deletions

diff --git a/Rakefile b/Rakefile
index 95f3469081..8d4e417095 100644
--- a/Rakefile
+++ b/Rakefile
@@ -136,7 +136,7 @@ begin
             if rg == "master"
               system("git checkout origin/master")
             else
-              system("git checkout #{rg}")
+              system("git checkout #{rg}") || raise("Unknown Rubygems ref #{rg}")
             end
             hash = `git rev-parse HEAD`.chomp
           end