diff --git a/fluxer_app/src/features/ui/state/Tick.test.ts b/fluxer_app/src/features/ui/state/Tick.test.ts
new file mode 100644
index 000000000..83b7f89a3
--- /dev/null
+++ b/fluxer_app/src/features/ui/state/Tick.test.ts
@@ -0,0 +1,65 @@
+// @vitest-environment happy-dom
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {autorun} from 'mobx';
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+
+async function loadTick() {
+	vi.resetModules();
+	const {default: Window} = await import('@app/features/window/state/Window');
+	const {default: Tick} = await import('@app/features/ui/state/Tick');
+	return {Tick, Window};
+}
+
+describe('Tick', () => {
+	beforeEach(() => {
+		vi.useFakeTimers();
+	});
+
+	afterEach(() => {
+		vi.useRealTimers();
+	});
+
+	it('keeps counting while the window is visible but not focused', async () => {
+		const {Tick, Window} = await loadTick();
+		const dispose = autorun(() => Tick.nowSecond);
+		const started = Tick.nowSecond;
+		Window.setFocused(false);
+		vi.advanceTimersByTime(3000);
+		expect(Window.visible).toBe(true);
+		expect(Tick.nowSecond).toBe(started + 3);
+		dispose();
+	});
+
+	it('stops counting while the window is hidden', async () => {
+		const {Tick, Window} = await loadTick();
+		const dispose = autorun(() => Tick.nowSecond);
+		Window.setVisible(false);
+		const stopped = Tick.nowSecond;
+		vi.advanceTimersByTime(5000);
+		expect(Tick.nowSecond).toBe(stopped);
+		dispose();
+	});
+
+	it('resynchronises to wall clock as soon as the window becomes visible again', async () => {
+		const {Tick, Window} = await loadTick();
+		const dispose = autorun(() => Tick.nowSecond);
+		Window.setVisible(false);
+		const stopped = Tick.nowSecond;
+		vi.advanceTimersByTime(60_000);
+		expect(Tick.nowSecond).toBe(stopped);
+		Window.setVisible(true);
+		expect(Tick.nowSecond).toBe(stopped + 60);
+		dispose();
+	});
+
+	it('does not run an interval while nothing observes the clock', async () => {
+		const {Tick} = await loadTick();
+		const idle = Tick.nowSecond;
+		vi.advanceTimersByTime(5000);
+		expect(Tick.nowSecond).toBe(idle);
+		const dispose = autorun(() => Tick.nowSecond);
+		expect(Tick.nowSecond).toBe(idle + 5);
+		dispose();
+	});
+});
diff --git a/fluxer_app/src/features/ui/state/Tick.ts b/fluxer_app/src/features/ui/state/Tick.ts
index 38abdd424..5f2cdaa41 100644
--- a/fluxer_app/src/features/ui/state/Tick.ts
+++ b/fluxer_app/src/features/ui/state/Tick.ts
@@ -20,9 +20,9 @@ class TickRegistryImpl {
 			this.stop();
 		});
 		reaction(
-			() => Window.focused,
-			(focused) => {
-				if (focused) this.start();
+			() => Window.visible,
+			(visible) => {
+				if (visible) this.start();
 				else this.stop();
 			},
 			{fireImmediately: true},
@@ -30,7 +30,7 @@ class TickRegistryImpl {
 	}
 
 	private start(): void {
-		if (!this.observed || !Window.focused || this.intervalId !== null) return;
+		if (!this.observed || !Window.visible || this.intervalId !== null) return;
 		this.tick();
 		this.intervalId = window.setInterval(() => this.tick(), 1000);
 	}