diff --git a/lib/paper_trail/attribute_serializers/cast_attribute_serializer.rb b/lib/paper_trail/attribute_serializers/cast_attribute_serializer.rb
index c597f869..f63bf2b6 100644
--- a/lib/paper_trail/attribute_serializers/cast_attribute_serializer.rb
+++ b/lib/paper_trail/attribute_serializers/cast_attribute_serializer.rb
@@ -6,8 +6,7 @@ module PaperTrail
     # to an attribute of type `ActiveRecord::Type::Integer`.
     #
     # This implementation depends on the `type_for_attribute` method, which was
-    # introduced in rails 4.2. In older versions of rails, we shim this method
-    # with `LegacyActiveRecordShim`.
+    # introduced in rails 4.2. As of PT 8, we no longer support rails < 4.2.
     class CastAttributeSerializer
       def initialize(klass)
         @klass = klass
diff --git a/lib/paper_trail/attribute_serializers/legacy_active_record_shim.rb b/lib/paper_trail/attribute_serializers/legacy_active_record_shim.rb
deleted file mode 100644
index e9928caa..00000000
--- a/lib/paper_trail/attribute_serializers/legacy_active_record_shim.rb
+++ /dev/null
@@ -1,48 +0,0 @@
-module PaperTrail
-  module AttributeSerializers
-    # Included into model if AR version is < 4.2. Backport Rails 4.2 and later's
-    # `type_for_attribute` so we can build on a common interface.
-    module LegacyActiveRecordShim
-      # An attribute which needs no processing. It is part of our backport (shim)
-      # of rails 4.2's attribute API. See `type_for_attribute` below.
-      class NoOpAttribute
-        def type_cast_for_database(value)
-          value
-        end
-
-        def type_cast_from_database(data)
-          data
-        end
-      end
-      NO_OP_ATTRIBUTE = NoOpAttribute.new
-
-      # An attribute which requires manual (de)serialization to/from what we get
-      # from the database. It is part of our backport (shim) of rails 4.2's
-      # attribute API. See `type_for_attribute` below.
-      class SerializedAttribute
-        def initialize(coder)
-          @coder = coder.respond_to?(:dump) ? coder : PaperTrail.serializer
-        end
-
-        def type_cast_for_database(value)
-          @coder.dump(value)
-        end
-
-        def type_cast_from_database(data)
-          @coder.load(data)
-        end
-      end
-
-      def type_for_attribute(attr_name)
-        serialized_attribute_types[attr_name.to_s] || NO_OP_ATTRIBUTE
-      end
-
-      def serialized_attribute_types
-        @attribute_types ||= Hash[serialized_attributes.map do |attr_name, coder|
-          [attr_name, SerializedAttribute.new(coder)]
-        end]
-      end
-      private :serialized_attribute_types
-    end
-  end
-end
diff --git a/lib/paper_trail/has_paper_trail.rb b/lib/paper_trail/has_paper_trail.rb
index d00aece2..0715dc49 100644
--- a/lib/paper_trail/has_paper_trail.rb
+++ b/lib/paper_trail/has_paper_trail.rb
@@ -1,5 +1,4 @@
 require "active_support/core_ext/object" # provides the `try` method
-require "paper_trail/attribute_serializers/legacy_active_record_shim"
 require "paper_trail/attribute_serializers/object_attribute"
 require "paper_trail/attribute_serializers/object_changes_attribute"
 require "paper_trail/model_config"
diff --git a/lib/paper_trail/model_config.rb b/lib/paper_trail/model_config.rb
index 25e8be53..da3b63bf 100644
--- a/lib/paper_trail/model_config.rb
+++ b/lib/paper_trail/model_config.rb
@@ -79,13 +79,6 @@ module PaperTrail
       options[:on] ||= %i[create update destroy]
       options[:on] = Array(options[:on]) # Support single symbol
       @model_class.send :include, ::PaperTrail::Model::InstanceMethods
-      if ::ActiveRecord::VERSION::STRING < "4.2"
-        ::ActiveSupport::Deprecation.warn(
-          "Your version of ActiveRecord (< 4.2) has reached EOL. PaperTrail " \
-          "will soon drop support. Please upgrade ActiveRecord ASAP."
-        )
-        @model_class.send :extend, AttributeSerializers::LegacyActiveRecordShim
-      end
       setup_options(options)
       setup_associations(options)
       setup_transaction_callbacks