diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/cast.rb b/activerecord/lib/active_record/connection_adapters/postgresql/cast.rb
index a865c5c310..b0a161ff32 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/cast.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/cast.rb
@@ -34,28 +34,12 @@ module ActiveRecord
           end
         end
 
-        def json_to_string(object) # :nodoc:
-          if Hash === object || Array === object
-            ActiveSupport::JSON.encode(object)
-          else
-            object
-          end
-        end
-
         def range_to_string(object) # :nodoc:
           from = object.begin.respond_to?(:infinite?) && object.begin.infinite? ? '' : object.begin
           to   = object.end.respond_to?(:infinite?) && object.end.infinite? ? '' : object.end
           "[#{from},#{to}#{object.exclude_end? ? ')' : ']'}"
         end
 
-        def string_to_json(string) # :nodoc:
-          if String === string
-            ActiveSupport::JSON.decode(string)
-          else
-            string
-          end
-        end
-
         private
 
           HstorePair = begin
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
index ab1165f301..e12ddd9901 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
@@ -10,11 +10,19 @@ module ActiveRecord
           end
 
           def type_cast_from_database(value)
-            ConnectionAdapters::PostgreSQLColumn.string_to_json(value)
+            if value.is_a?(::String)
+              ::ActiveSupport::JSON.decode(value)
+            else
+              super
+            end
           end
 
           def type_cast_for_database(value)
-            ConnectionAdapters::PostgreSQLColumn.json_to_string(value)
+            if value.is_a?(::Array) || value.is_a?(::Hash)
+              ::ActiveSupport::JSON.encode(value)
+            else
+              super
+            end
           end
 
           def accessor
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
index 4caed77952..2818633495 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
@@ -30,14 +30,12 @@ module ActiveRecord
           when Array
             case sql_type
             when 'point' then super(PostgreSQLColumn.point_to_string(value))
-            when 'json' then super(PostgreSQLColumn.json_to_string(value))
             else
               super(value, array_column(column))
             end
           when Hash
             case sql_type
             when 'hstore' then super(PostgreSQLColumn.hstore_to_string(value), column)
-            when 'json' then super(PostgreSQLColumn.json_to_string(value), column)
             else super
             end
           when Float
@@ -92,14 +90,12 @@ module ActiveRecord
           when Array
             case column.sql_type
             when 'point' then PostgreSQLColumn.point_to_string(value)
-            when 'json' then PostgreSQLColumn.json_to_string(value)
             else
               super(value, array_column(column))
             end
           when Hash
             case column.sql_type
             when 'hstore' then PostgreSQLColumn.hstore_to_string(value, array_member)
-            when 'json' then PostgreSQLColumn.json_to_string(value)
             else super(value, column)
             end
           else
diff --git a/activerecord/test/cases/adapters/postgresql/json_test.rb b/activerecord/test/cases/adapters/postgresql/json_test.rb
index e44afea33a..50135151c2 100644
--- a/activerecord/test/cases/adapters/postgresql/json_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/json_test.rb
@@ -77,7 +77,7 @@ class PostgresqlJSONTest < ActiveRecord::TestCase
     column = JsonDataType.columns_hash["payload"]
 
     data = "{\"a_key\":\"a_value\"}"
-    hash = column.class.string_to_json data
+    hash = column.type_cast_from_database(data)
     assert_equal({'a_key' => 'a_value'}, hash)
     assert_equal({'a_key' => 'a_value'}, column.type_cast_from_database(data))