diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 4762c7d21ddf01fe91f076076fc26b92ab1aa126..904dab0e05100df47e106d37330696ca23b9a8a6 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,30 @@
+*   Handle `TZInfo::AmbiguousTime` errors
+
+    Make `ActiveSupport::TimeWithZone` match Ruby's handling of ambiguous
+    times by choosing the later period, e.g.
+
+    Ruby:
+    ```
+    ENV["TZ"] = "Europe/Moscow"
+    Time.local(2014, 10, 26, 1, 0, 0)   # => 2014-10-26 01:00:00 +0300
+    ```
+
+    Before:
+    ```
+    >> "2014-10-26 01:00:00".in_time_zone("Moscow")
+    TZInfo::AmbiguousTime: 26/10/2014 01:00 is an ambiguous local time.
+    ```
+
+    After:
+    ```
+    >> "2014-10-26 01:00:00".in_time_zone("Moscow")
+    => Sun, 26 Oct 2014 01:00:00 MSK +03:00
+    ```
+
+    Fixes #17395.
+
+    *Andrew White*
+
 *   Redis cache store.
 
     ```
diff --git a/activesupport/lib/active_support/values/time_zone.rb b/activesupport/lib/active_support/values/time_zone.rb
index d1a20030132f6b944d6e86daf76a3d601dc146d5..b294d99fe0e187960ed8fa20d045e7ef5a4bdb9b 100644
--- a/activesupport/lib/active_support/values/time_zone.rb
+++ b/activesupport/lib/active_support/values/time_zone.rb
@@ -506,7 +506,7 @@ def period_for_utc(time)
     # Available so that TimeZone instances respond like TZInfo::Timezone
     # instances.
     def period_for_local(time, dst = true)
-      tzinfo.period_for_local(time, dst)
+      tzinfo.period_for_local(time, dst) { |periods| periods.last }
     end
 
     def periods_for_local(time) #:nodoc:
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 0f80a247582cd132b4d71158745948de14b16004..ab965689568f3a69fa3773deb72ec4f5fd836f4f 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -50,6 +50,12 @@ def test_in_time_zone_with_bad_argument
     assert_raise(ArgumentError) { @twz.in_time_zone(Object.new) }
   end
 
+  def test_in_time_zone_with_ambiguous_time
+    with_env_tz "Europe/Moscow" do
+      assert_equal Time.utc(2014, 10, 25, 22, 0, 0), Time.local(2014, 10, 26, 1, 0, 0).in_time_zone("Moscow")
+    end
+  end
+
   def test_localtime
     assert_equal @twz.localtime, @twz.utc.getlocal
     assert_instance_of Time, @twz.localtime
@@ -1301,4 +1307,10 @@ def test_in_time_zone_with_invalid_argument
     assert_raise(ArgumentError) { @u.in_time_zone(Object.new) }
     assert_raise(ArgumentError) { @z.in_time_zone(Object.new) }
   end
+
+  def test_in_time_zone_with_ambiguous_time
+    with_tz_default "Moscow" do
+      assert_equal Time.utc(2014, 10, 25, 22, 0, 0), "2014-10-26 01:00:00".in_time_zone
+    end
+  end
 end
diff --git a/activesupport/test/time_zone_test.rb b/activesupport/test/time_zone_test.rb
index acb0ecd226a663c9e4c1db2474d35f278ffc9ea8..862e8724948adcf4e9d288db7cc60df01553ec1b 100644
--- a/activesupport/test/time_zone_test.rb
+++ b/activesupport/test/time_zone_test.rb
@@ -32,6 +32,12 @@ def test_period_for_local
     end
   end
 
+  def test_period_for_local_with_ambigiuous_time
+    zone = ActiveSupport::TimeZone["Moscow"]
+    period = zone.period_for_local(Time.utc(2015, 1, 1))
+    assert_equal period, zone.period_for_local(Time.utc(2014, 10, 26, 1, 0, 0))
+  end
+
   def test_from_integer_to_map
     assert_instance_of ActiveSupport::TimeZone, ActiveSupport::TimeZone[-28800] # PST
   end
@@ -195,6 +201,11 @@ def test_local_enforces_fall_dst_rules
     assert_equal "EDT", twz.zone
   end
 
+  def test_local_with_ambiguous_time
+    zone = ActiveSupport::TimeZone["Moscow"]
+    assert_equal Time.utc(2014, 10, 25, 22, 0, 0), zone.local(2014, 10, 26, 1, 0, 0)
+  end
+
   def test_at
     zone = ActiveSupport::TimeZone["Eastern Time (US & Canada)"]
     secs = 946684800.0
@@ -303,6 +314,11 @@ def test_iso8601_handles_dst_jump
     end
   end
 
+  def test_iso8601_with_ambiguous_time
+    zone = ActiveSupport::TimeZone["Moscow"]
+    assert_equal Time.utc(2014, 10, 25, 22, 0, 0), zone.parse("2014-10-26T01:00:00")
+  end
+
   def test_parse
     zone = ActiveSupport::TimeZone["Eastern Time (US & Canada)"]
     twz = zone.parse("1999-12-31 19:00:00")
@@ -412,6 +428,11 @@ def test_parse_with_invalid_date
     assert_equal "argument out of range", exception.message
   end
 
+  def test_parse_with_ambiguous_time
+    zone = ActiveSupport::TimeZone["Moscow"]
+    assert_equal Time.utc(2014, 10, 25, 22, 0, 0), zone.parse("2014-10-26 01:00:00")
+  end
+
   def test_rfc3339
     zone = ActiveSupport::TimeZone["Eastern Time (US & Canada)"]
     twz = zone.rfc3339("1999-12-31T14:00:00-10:00")
@@ -604,6 +625,11 @@ def test_strptime_with_timestamp_milliseconds
     end
   end
 
+  def test_strptime_with_ambiguous_time
+    zone = ActiveSupport::TimeZone["Moscow"]
+    assert_equal Time.utc(2014, 10, 25, 22, 0, 0), zone.strptime("2014-10-26 01:00:00", "%Y-%m-%d %H:%M:%S")
+  end
+
   def test_utc_offset_lazy_loaded_from_tzinfo_when_not_passed_in_to_initialize
     tzinfo = TZInfo::Timezone.get("America/New_York")
     zone = ActiveSupport::TimeZone.create(tzinfo.name, nil, tzinfo)