diff --git a/static/app.js b/static/app.js
index 5b99457..31f214e 100644
--- a/static/app.js
+++ b/static/app.js
@@ -446,6 +446,22 @@ async function showAnime(slug_id, opts = {}) {
     anB.classList.toggle("on", autoNext);
   };
   const ctl = [langBtn, spd, prevB, nextB, fillB, jump, anB];
+  const fsB = el("button", "tiny", "\u26f6 full");
+  fsB.title = "fullscreen";
+  fsB.onclick = () => {
+    const v = document.querySelector("#player video");
+    if (!v) return;
+    if (document.fullscreenElement || document.webkitFullscreenElement) {
+      (document.exitFullscreen || document.webkitExitFullscreen).call(document);
+      return;
+    }
+    // native Fullscreen API: the video fills the window (and scales with it);
+    // iOS Safari has no element fullscreen, so fall back to its in-player one
+    if (v.requestFullscreen) v.requestFullscreen();
+    else if (v.webkitEnterFullscreen) v.webkitEnterFullscreen();
+    else if (v.webkitRequestFullscreen) v.webkitRequestFullscreen();
+  };
+  ctl.push(fsB);
   if (document.pictureInPictureEnabled) {
     const pipB = el("button", "tiny", "\u29c9 PiP");
     pipB.title = "picture-in-picture";
diff --git a/tests/test_browser.py b/tests/test_browser.py
index 2e0d8e3..07026e1 100644
--- a/tests/test_browser.py
+++ b/tests/test_browser.py
@@ -490,3 +490,31 @@ async def _stale_history_remap_board():
             "location.search.includes('q=')", timeout=15000, polling=POLL)
         assert not errors, errors
         await browser.close()
+
+
+def test_fullscreen_toggle():
+    asyncio.run(_fullscreen_toggle())
+
+
+async def _fullscreen_toggle():
+    # the player controls get a fullscreen button; in headless chromium the
+    # native API works, so exercise enter + exit.
+    async with async_playwright() as p:
+        browser = await p.chromium.launch(args=LAUNCH_ARGS)
+        page = await (await browser.new_context()).new_page()
+        errors = []
+        page.on("pageerror", lambda e: errors.append(str(e)))
+        await _login(page, "admin", "adminpw12345")
+        await page.goto(BASE + "/?anime=chainsaw-man-922")
+        btn = page.locator("button:has-text('full')")
+        await btn.wait_for(timeout=30000)
+        assert await page.evaluate(
+            "() => typeof document.querySelector('#player video').requestFullscreen === 'function'")
+        await btn.click(force=True)
+        await page.wait_for_function(
+            "() => !!document.fullscreenElement", timeout=15000, polling=POLL)
+        await btn.click(force=True)
+        await page.wait_for_function(
+            "() => !document.fullscreenElement", timeout=15000, polling=POLL)
+        assert not errors, errors
+        await browser.close()