diff --git a/test/functional/auth_sources_controller_test.rb b/test/functional/auth_sources_controller_test.rb
index e462f669..e79fa933 100644
--- a/test/functional/auth_sources_controller_test.rb
+++ b/test/functional/auth_sources_controller_test.rb
@@ -14,6 +14,12 @@
 
 require File.expand_path('../../test_helper', __FILE__)
 
+# Remove to_s on the TreeNode. This would cause an error on Ruby 1.9 as the
+# method has a bug preventing it to return strings. It is implicitly called by
+# shoulda during an inspect on Ruby 1.9 only. The bug is reported at
+# http://rubyforge.org/tracker/index.php?func=detail&aid=29435&group_id=1215&atid=4793
+Tree::TreeNode.class_eval {remove_method :to_s}
+
 class AuthSourcesControllerTest < ActionController::TestCase
   fixtures :all