diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index <HASH>..<HASH> 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -3,6 +3,10 @@ $LOAD_PATH << File.expand_path('../../spec/helpers', __FILE__)
 require 'buildpack/packager'
 require 'file_system_helpers'
 
+unless system("which tree")
+  raise "Please install the `tree` commandline tool."
+end
+
 RSpec.configure do |config|
   config.include FileSystemHelpers
 end
Check for existence of `tree` before running suite.