diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 9dbed2c1b770897e067823f15dae2e9a143f66c3..39af3a02cf2ecf12b5951ccb896bdf4396955be6 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -844,6 +844,10 @@ def version_string(full_version_string)
           full_version_string.match(/^(?:5\.5\.5-)?(\d+\.\d+\.\d+)/)[1]
         end
 
+        # Alias MysqlString to work Mashal.load(File.read("legacy_record.dump")).
+        # TODO: Remove the constant alias once Rails 6.1 has released.
+        MysqlString = Type::String # :nodoc:
+
         ActiveRecord::Type.register(:immutable_string, adapter: :mysql2) do |_, **args|
           Type::ImmutableString.new(true: "1", false: "0", **args)
         end
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index f8f3e86acc9c134a80c21f368ed5c1da87fdc5db..5e948224d7f22d7189ca09c1e3b3cca24d403923 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -1226,6 +1226,21 @@ def test_marshalling_with_associations
     assert_equal 1, post.comments.length
   end
 
+  if current_adapter?(:Mysql2Adapter)
+    def test_marshal_load_legacy_6_0_record_mysql
+      path = File.expand_path(
+        "support/marshal_compatibility_fixtures/legacy_6_0_record_mysql.dump",
+        TEST_ROOT
+      )
+      topic = Marshal.load(File.read(path))
+
+      assert_not_predicate topic, :new_record?
+      assert_equal 1, topic.id
+      assert_equal "The First Topic", topic.title
+      assert_equal "Have a nice day", topic.content
+    end
+  end
+
   if Process.respond_to?(:fork) && !in_memory_db?
     def test_marshal_between_processes
       # Define a new model to ensure there are no caches
diff --git a/activerecord/test/support/marshal_compatibility_fixtures/legacy_6_0_record_mysql.dump b/activerecord/test/support/marshal_compatibility_fixtures/legacy_6_0_record_mysql.dump
new file mode 100644
index 0000000000000000000000000000000000000000..72ebbd88d0ea24dcfa68b94ea4cbd865cc1dd699
Binary files /dev/null and b/activerecord/test/support/marshal_compatibility_fixtures/legacy_6_0_record_mysql.dump differ