diff --git a/actionpack/lib/action_controller/assertions.rb b/actionpack/lib/action_controller/assertions.rb
index 00811d24d55bb..999edc1440b9c 100644
--- a/actionpack/lib/action_controller/assertions.rb
+++ b/actionpack/lib/action_controller/assertions.rb
@@ -304,7 +304,7 @@ def assert_dom_not_equal(expected, actual, message="")
       # ensures that the passed record is valid by active record standards. returns the error messages if not
       def assert_valid(record)                                   
         clean_backtrace do
-          assert record.valid?, record.errors.full_messages        
+          assert record.valid?, record.errors.full_messages.join("\n")
         end
       end