diff --git a/activesupport/test/core_ext/string_ext_test.rb b/activesupport/test/core_ext/string_ext_test.rb
index <HASH>..<HASH> 100644
--- a/activesupport/test/core_ext/string_ext_test.rb
+++ b/activesupport/test/core_ext/string_ext_test.rb
@@ -414,7 +414,7 @@ class StringConversionsTest < ActiveSupport::TestCase
   end
 
   def test_partial_string_to_time
-    with_env_tz "Europe/Moscow" do
+    with_env_tz "Europe/Moscow" do # use timezone which does not observe DST.
       now = Time.now
       assert_equal Time.local(now.year, now.month, now.day, 23, 50), "23:50".to_time
       assert_equal Time.utc(now.year, now.month, now.day, 23, 50), "23:50".to_time(:utc)
tests, add note about the usage of a specific timezone. Closes #<I>.