2 files changed, 30 insertions, 0 deletions
diff --git a/actionpack/lib/action_controller/metal/strong_parameters.rb b/actionpack/lib/action_controller/metal/strong_parameters.rb
index b326695ce2..fea04d98e0 100644
--- a/actionpack/lib/action_controller/metal/strong_parameters.rb
+++ b/actionpack/lib/action_controller/metal/strong_parameters.rb
@@ -783,6 +783,11 @@ module ActionController
           end
         end
       end
+
+      def initialize_copy(source)
+        super
+        @parameters = source.instance_variable_get(:@parameters).dup
+      end
   end
 
   # == Strong \Parameters
diff --git a/actionpack/test/controller/parameters/dup_test.rb b/actionpack/test/controller/parameters/dup_test.rb
new file mode 100644
index 0000000000..cf273933bd
--- /dev/null
+++ b/actionpack/test/controller/parameters/dup_test.rb
@@ -0,0 +1,25 @@
+require 'abstract_unit'
+require 'action_controller/metal/strong_parameters'
+
+class ParametersDupTest < ActiveSupport::TestCase
+  setup do
+    ActionController::Parameters.permit_all_parameters = false
+
+    @params = ActionController::Parameters.new(
+      person: {
+        age: '32',
+        name: {
+          first: 'David',
+          last: 'Heinemeier Hansson'
+        },
+        addresses: [{city: 'Chicago', state: 'Illinois'}]
+      }
+    )
+  end
+
+  test "changes on a duplicate do not affect the original" do
+    dupped_params = @params.dup
+    dupped_params.delete(:person)
+    assert_not_equal @params, dupped_params
+  end
+end