diff --git a/app/helpers/attachments_helper.rb b/app/helpers/attachments_helper.rb
index 5e391ee6a9e..b0977f0e10b 100644
--- a/app/helpers/attachments_helper.rb
+++ b/app/helpers/attachments_helper.rb
@@ -60,14 +60,15 @@ def attachment_component_params(attachment, alternative_format_contact_email: ni
   end
 
   def block_attachments(attachments = [], alternative_format_contact_email = nil)
-    attachments
-      .select { |attachment| !attachment.file? || attachment.attachment_data.all_asset_variants_uploaded? }
-      .map do |attachment|
+    filtered_attachments = attachments.select { |attachment| !attachment.file? || attachment.attachment_data.all_asset_variants_uploaded? }
+    filtered_attachments_size = filtered_attachments.size
+    filtered_attachments.each_with_index.map do |attachment, index|
       render(
         partial: "govuk_publishing_components/components/attachment",
         locals: {
           attachment: attachment_component_params(attachment, alternative_format_contact_email:),
           margin_bottom: 6,
+          details_ga4_attributes: { index_section: index + 1, index_section_count: filtered_attachments_size },
         },
       )
     end
diff --git a/test/unit/app/helpers/attachments_helper_test.rb b/test/unit/app/helpers/attachments_helper_test.rb
index e9abae7fe59..ae116f6af5c 100644
--- a/test/unit/app/helpers/attachments_helper_test.rb
+++ b/test/unit/app/helpers/attachments_helper_test.rb
@@ -41,6 +41,25 @@ class AttachmentsHelperTest < ActionView::TestCase
     end
   end
 
+  test "block_attachments renders with GA4 indexes on the nested details component" do
+    alternative_format_contact_email = "test@example.com"
+    file_attachment_with_all_assets = create(:file_attachment)
+    attachments = [
+      file_attachment_with_all_assets,
+      file_attachment_with_all_assets,
+      file_attachment_with_all_assets,
+    ]
+
+    rendered_attachments = block_attachments(attachments, alternative_format_contact_email)
+    rendered_attachments.each.with_index do |rendered, index|
+      assert_select_within_html(rendered, ".gem-c-details") do |details|
+        ga4_event = JSON.parse(details.attribute("data-ga4-event"))
+        assert_equal ga4_event["index_section"], index + 1
+        assert_equal ga4_event["index_section_count"], 3
+      end
+    end
+  end
+
   test "component params for HTML attachment" do
     attachment = create(:html_attachment)
     expect_params = {