diff --git a/lib/rdoc/test_case.rb b/lib/rdoc/test_case.rb
index 99d4bd4ee1..245e4ef1c5 100644
--- a/lib/rdoc/test_case.rb
+++ b/lib/rdoc/test_case.rb
@@ -1,7 +1,7 @@
 require 'rubygems'
 
 begin
-  gem 'minitest', '~> 4.0'
+  gem 'minitest', '~> 4.0' unless defined?(Test::Unit)
 rescue NoMethodError
   # for ruby tests
 end