2 files changed, 6 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index 3549cbb090..c129dc8c52 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -92,11 +92,7 @@ module ActiveRecord
         end
 
         def internal_attribute_access_code(attr_name, cast_code)
-          if attr_name == primary_key
-            access_code = "v = @attributes[attr_name];"
-          else
-            access_code = "v = @attributes.fetch(attr_name) { missing_attribute(attr_name, caller) };"
-          end
+          access_code = "v = @attributes.fetch(attr_name) { missing_attribute(attr_name, caller) };"
 
           access_code << "v && #{cast_code};"
 
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index adba3f710c..a774af6024 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -202,6 +202,7 @@ module ActiveRecord
       cloned_attributes.delete(self.class.primary_key)
 
       @attributes = cloned_attributes
+      @attributes[self.class.primary_key] = nil
 
       run_callbacks(:initialize) if _initialize_callbacks.any?
 
@@ -326,6 +327,10 @@ module ActiveRecord
     end
 
     def init_internals
+      pk = self.class.primary_key
+
+      @attributes[pk] = nil unless @attributes.key?(pk)
+
       @relation               = nil
       @aggregation_cache      = {}
       @association_cache      = {}