diff --git a/tests/e2e/declare_repos_test.go b/tests/e2e/declare_repos_test.go
index 23bc023b70..85e3fcbda8 100644
--- a/tests/e2e/declare_repos_test.go
+++ b/tests/e2e/declare_repos_test.go
@@ -6,6 +6,7 @@ package e2e
 import (
 	"fmt"
 	"os"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -144,6 +145,34 @@ body:
 			addCommitToBranch(t, user, repo, "test-branch", "test-branch", "test-README.md", commit2Sha,
 				readStringFile(t, "tests/e2e/declarative-repo/long-diff-test/3-README.md"))
 		}),
+		newRepo(t, 2, "huge-diff-test", nil, []FileChanges{{
+			Filename: "glossary.po",
+			Versions: []string{
+				func() string {
+					var sb strings.Builder
+					sb.Write([]byte("0"))
+					for i := 1; i < 2000; i++ {
+						sb.WriteString(strconv.Itoa(i))
+						sb.WriteByte('\n')
+					}
+					return sb.String()
+				}(),
+			},
+		}}, func(user *user_model.User, repo *repo_model.Repository) {
+			addCommitToBranch(t, user, repo, "main", "main-2", "glossary.po", "",
+				func() string {
+					var sb strings.Builder
+					sb.Write([]byte("0"))
+					for i := 1; i < 2000; i++ {
+						sb.WriteString(strconv.Itoa(i))
+						if i%12 == 0 {
+							sb.WriteString("Blub")
+						}
+						sb.WriteByte('\n')
+					}
+					return sb.String()
+				}())
+		}),
 		// add your repo declarations here
 	}
 
diff --git a/tests/e2e/file-diff.test.e2e.ts b/tests/e2e/file-diff.test.e2e.ts
new file mode 100644
index 0000000000..f6c398e009
--- /dev/null
+++ b/tests/e2e/file-diff.test.e2e.ts
@@ -0,0 +1,41 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// @watch start
+// templates/repo/diff/**
+// web_src/css/review.css
+// web_src/js/features/repo-diff.js
+// @watch end
+
+import {expect} from '@playwright/test';
+import {test} from './utils_e2e.ts';
+
+test.use({user: 'user2'});
+
+test('Expand Large diff', async ({page}) => {
+  let response = await page.goto('/user2/huge-diff-test/src/branch/main-2', {waitUntil: 'domcontentloaded'});
+  expect(response?.status()).toBe(200);
+
+  const commitUrl = await page.locator('.commit-summary a').getAttribute('href');
+
+  response = await page.goto(commitUrl, {waitUntil: 'domcontentloaded'});
+  expect(response?.status()).toBe(200);
+
+  const loadDiff = page.locator('.diff-load-button');
+  const expandDiff = page.locator('.code-expander-button');
+  const diffLines = page.locator('.file-body tbody > tr');
+
+  await expect(loadDiff).toBeVisible();
+
+  loadDiff.click();
+  await page.waitForLoadState('load');
+
+  await expect(expandDiff).toHaveCount(167);
+  await expect(diffLines).toHaveCount(1495);
+
+  await expandDiff.first().click();
+  await page.waitForLoadState('load');
+
+  await expect(expandDiff).toHaveCount(166);
+  await expect(diffLines).toHaveCount(1502);
+});
diff --git a/web_src/js/features/repo-diff.js b/web_src/js/features/repo-diff.js
index 9b62b9f94f..02481be853 100644
--- a/web_src/js/features/repo-diff.js
+++ b/web_src/js/features/repo-diff.js
@@ -1,4 +1,5 @@
 import $ from 'jquery';
+import htmx from 'htmx.org';
 import {initCompReactionSelector} from './comp/ReactionSelector.js';
 import {initRepoIssueContentHistory} from './repo-issue-content.js';
 import {initDiffFileTree} from './repo-diff-filetree.js';
@@ -151,6 +152,7 @@ function onShowMoreFiles() {
   initViewedCheckboxListenerFor();
   countAndUpdateViewedFiles();
   initImageDiff();
+  htmx.process(document.body);
 }
 
 export async function loadMoreFiles(url) {