diff --git a/activesupport/lib/active_support/core_ext/date_time/zones.rb b/activesupport/lib/active_support/core_ext/date_time/zones.rb
index 98565e67506e0e0355077cfac978ab41b52a9be8..6002d4ad2aa57354a2c2b591f42528923c2facaf 100644
--- a/activesupport/lib/active_support/core_ext/date_time/zones.rb
+++ b/activesupport/lib/active_support/core_ext/date_time/zones.rb
@@ -12,6 +12,8 @@ class DateTime
   #
   #   DateTime.new(2000).in_time_zone('Alaska')  # => Fri, 31 Dec 1999 15:00:00 AKST -09:00
   def in_time_zone(zone = ::Time.zone)
+    return self unless zone
+
     ActiveSupport::TimeWithZone.new(utc? ? self : getutc, ::Time.__send__(:get_zone, zone))
   end
 end
diff --git a/activesupport/lib/active_support/core_ext/time/zones.rb b/activesupport/lib/active_support/core_ext/time/zones.rb
index adc9fe382431ad1d14337bc6bf4b0c32b8d14cd4..a02402aa3fef8425d54196e4aa9f91e3c9b8f9ef 100644
--- a/activesupport/lib/active_support/core_ext/time/zones.rb
+++ b/activesupport/lib/active_support/core_ext/time/zones.rb
@@ -73,6 +73,8 @@ def get_zone(time_zone)
   #
   #   Time.utc(2000).in_time_zone('Alaska')  # => Fri, 31 Dec 1999 15:00:00 AKST -09:00
   def in_time_zone(zone = ::Time.zone)
+    return self unless zone
+
     ActiveSupport::TimeWithZone.new(utc? ? self : getutc, ::Time.__send__(:get_zone, zone))
   end
 end
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 2cf5bd6ea97b032328941f46ed3f37bd50d67949..cf11f4d28f76102df5047af9e184fdefc995a954 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -737,6 +737,13 @@ def test_in_time_zone
     end
   end
 
+  def test_nil_time_zone
+    Time.use_zone nil do
+      assert !@t.in_time_zone.respond_to?(:period), 'no period method'
+      assert !@dt.in_time_zone.respond_to?(:period), 'no period method'
+    end
+  end
+
   def test_in_time_zone_with_argument
     Time.use_zone 'Eastern Time (US & Canada)' do # Time.zone will not affect #in_time_zone(zone)
       assert_equal 'Fri, 31 Dec 1999 15:00:00 AKST -09:00', @t.in_time_zone('Alaska').inspect