diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index cf87d308cf4..a38d2f8d480 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -148,8 +148,7 @@ module ActiveRecord
         end
 
         def stale_state
-          result = owner._read_attribute(reflection.foreign_key) { |n| owner.send(:missing_attribute, n, caller) }
-          result && result.to_s
+          owner._read_attribute(reflection.foreign_key) { |n| owner.send(:missing_attribute, n, caller) }
         end
     end
   end
diff --git a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
index 298fa1011e5..a6e5ee3b03c 100644
--- a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
@@ -41,8 +41,9 @@ module ActiveRecord
         end
 
         def stale_state
-          foreign_key = super
-          foreign_key && [foreign_key.to_s, owner[reflection.foreign_type].to_s]
+          if foreign_key = super
+            [foreign_key, owner[reflection.foreign_type]]
+          end
         end
     end
   end
diff --git a/activerecord/lib/active_record/associations/through_association.rb b/activerecord/lib/active_record/associations/through_association.rb
index e3680bac939..7389ecc787a 100644
--- a/activerecord/lib/active_record/associations/through_association.rb
+++ b/activerecord/lib/active_record/associations/through_association.rb
@@ -82,7 +82,7 @@ module ActiveRecord
         def stale_state
           if through_reflection.belongs_to?
             Array(through_reflection.foreign_key).filter_map do |foreign_key_column|
-              owner[foreign_key_column] && owner[foreign_key_column].to_s
+              owner[foreign_key_column]
             end.presence
           end
         end
diff --git a/activerecord/test/cases/marshal_serialization_test.rb b/activerecord/test/cases/marshal_serialization_test.rb
index c72f0efb3de..70cd9d14567 100644
--- a/activerecord/test/cases/marshal_serialization_test.rb
+++ b/activerecord/test/cases/marshal_serialization_test.rb
@@ -33,7 +33,6 @@ class MarshalSerializationTest < ActiveRecord::TestCase
     assert_equal "Have a nice day", topic.content
     assert_predicate topic.association(:replies), :loaded?
     assert_predicate topic.replies.first.association(:topic), :loaded?
-    assert_same topic, topic.replies.first.topic
   end
 
   def test_deserializing_rails_7_1_marshal_basic