diff --git a/test/spec_mock.rb b/test/spec_mock.rb
index 73077fcc3..08e3a4570 100644
--- a/test/spec_mock.rb
+++ b/test/spec_mock.rb
@@ -3,6 +3,9 @@
 require_relative 'helper'
 require 'yaml'
 
+# Work correctly with older versions of Psych, having
+# unsafe_load call load (in older versions, load operates
+# as unsafe_load in current version).
 unless YAML.respond_to?(:unsafe_load)
   def YAML.unsafe_load(body)
     load(body)