diff --git a/activestorage/lib/active_storage/attached/one.rb b/activestorage/lib/active_storage/attached/one.rb
index 0244232b2ca498698ca52d569398e66c71acb0cf..e3600dc24122f218f83d12ae194c278ba7f7c849 100644
--- a/activestorage/lib/active_storage/attached/one.rb
+++ b/activestorage/lib/active_storage/attached/one.rb
@@ -64,12 +64,16 @@ def purge_later
 
     private
       def replace(attachable)
-        blob.tap do
+        unless attachable == blob
+          previous_blob = blob
+
           transaction do
             detach
             write_attachment build_attachment_from(attachable)
           end
-        end.purge_later
+
+          previous_blob.purge_later
+        end
       end
 
       def build_attachment_from(attachable)
diff --git a/activestorage/test/models/attachments_test.rb b/activestorage/test/models/attachments_test.rb
index 9ba2759893cef4c9cf7899499f72a1cf35958ed4..4c6b3e60005b05ed1cee95b062099763bdc792ea 100644
--- a/activestorage/test/models/attachments_test.rb
+++ b/activestorage/test/models/attachments_test.rb
@@ -56,6 +56,18 @@ class ActiveStorage::AttachmentsTest < ActiveSupport::TestCase
     assert ActiveStorage::Blob.service.exist?(@user.avatar.key)
   end
 
+  test "replace attached blob with itself" do
+    @user.avatar.attach create_blob(filename: "funky.jpg")
+
+    assert_no_changes -> { @user.reload.avatar.blob } do
+      assert_no_changes -> { @user.reload.avatar.attachment } do
+        assert_no_enqueued_jobs do
+          @user.avatar.attach @user.avatar.blob
+        end
+      end
+    end
+  end
+
   test "attach blob to new record" do
     user = User.new(name: "Jason")