diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 83ff80e31a..fac91c31da 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,23 @@
+*   Ensure duration parsing is consistent across DST changes
+
+    Previously `ActiveSupport::Duration.parse` used `Time.current` and
+    `Time#advance` to calculate the number of seconds in the duration
+    from an arbitrary collection of parts. However as `advance` tries to
+    be consistent across DST boundaries this meant that either the
+    duration was shorter or longer depending on the time of year.
+
+    This was fixed by using an absolute reference point in UTC which
+    isn't subject to DST transitions. An arbitrary date of Jan 1st, 2000
+    was chosen for no other reason that it seemed appropriate.
+
+    Additionally, duration parsing should now be marginally faster as we
+    are no longer creating instances of `ActiveSupport::TimeWithZone`
+    every time we parse a duration string.
+
+    Fixes #26941.
+
+    *Andrew White*
+
 *   Use `Hash#compact` and `Hash#compact!` from Ruby 2.4. Old Ruby versions
     will continue to get these methods from Active Support as before.
 
diff --git a/activesupport/lib/active_support/duration.rb b/activesupport/lib/active_support/duration.rb
index 862dabb1e8..82322291d0 100644
--- a/activesupport/lib/active_support/duration.rb
+++ b/activesupport/lib/active_support/duration.rb
@@ -7,6 +7,8 @@ module ActiveSupport
   #
   #   1.month.ago       # equivalent to Time.now.advance(months: -1)
   class Duration
+    EPOCH = ::Time.utc(2000)
+
     attr_accessor :value, :parts
 
     autoload :ISO8601Parser,     "active_support/duration/iso8601_parser"
@@ -140,8 +142,7 @@ module ActiveSupport
     # If invalid string is provided, it will raise +ActiveSupport::Duration::ISO8601Parser::ParsingError+.
     def self.parse(iso8601duration)
       parts = ISO8601Parser.new(iso8601duration).parse!
-      time  = ::Time.current
-      new(time.advance(parts) - time, parts)
+      new(EPOCH.advance(parts) - EPOCH, parts)
     end
 
     # Build ISO 8601 Duration string for this duration.
diff --git a/activesupport/test/core_ext/duration_test.rb b/activesupport/test/core_ext/duration_test.rb
index 53575272e3..c8e8b8a350 100644
--- a/activesupport/test/core_ext/duration_test.rb
+++ b/activesupport/test/core_ext/duration_test.rb
@@ -322,4 +322,35 @@ class DurationTest < ActiveSupport::TestCase
       assert_equal time + duration, time + ActiveSupport::Duration.parse(duration.iso8601), pattern.inspect
     end
   end
+
+  def test_iso8601_parsing_across_spring_dst_boundary
+    with_env_tz eastern_time_zone do
+      with_tz_default "Eastern Time (US & Canada)" do
+        travel_to Time.utc(2016, 3, 11) do
+          assert_equal 604800, ActiveSupport::Duration.parse("P7D").to_i
+          assert_equal 604800, ActiveSupport::Duration.parse("P1W").to_i
+        end
+      end
+    end
+  end
+
+  def test_iso8601_parsing_across_autumn_dst_boundary
+    with_env_tz eastern_time_zone do
+      with_tz_default "Eastern Time (US & Canada)" do
+        travel_to Time.utc(2016, 11, 4) do
+          assert_equal 604800, ActiveSupport::Duration.parse("P7D").to_i
+          assert_equal 604800, ActiveSupport::Duration.parse("P1W").to_i
+        end
+      end
+    end
+  end
+
+  private
+    def eastern_time_zone
+      if Gem.win_platform?
+        "EST5EDT"
+      else
+        "America/New_York"
+      end
+    end
 end