diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index e2eebfa41..678b958a9 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -319,10 +319,11 @@ module ApplicationHelper
 
   def thumbnail_tag(attachment)
     thumbnail_size = Setting.thumbnails_size.to_i
+    physical_thumbnail_size = thumbnail_size * 2
     link_to(
       image_tag(
-        thumbnail_path(attachment),
-        :srcset => "#{thumbnail_path(attachment, :size => thumbnail_size * 2)} 2x",
+        thumbnail_path(attachment, :size => physical_thumbnail_size),
+        :srcset => "#{thumbnail_path(attachment, :size => physical_thumbnail_size)} 2x",
         :style => "max-width: #{thumbnail_size}px; max-height: #{thumbnail_size}px;",
         :loading => "lazy"
       ),
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 452892e8b..64ef8a2de 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -1886,7 +1886,7 @@ class ApplicationHelperTest < Redmine::HelperTest
     assert_select_in(
       thumbnail_tag(a),
       'a[href=?][title=?] img[src=?][loading="lazy"]',
-      "/attachments/3", "logo.gif", "/attachments/thumbnail/3")
+      "/attachments/3", "logo.gif", "/attachments/thumbnail/3/200")
   end
 
   def test_link_to_project