The Jumping Dock Phenomenon
If you use a multi-monitor setup with your Mac, you may have noticed a confusing behavior: the macOS Dock (the bar containing all your app icons) refuses to stay on your primary screen. If you move your mouse to the bottom of your secondary, external monitor to click a low window border, the entire Dock suddenly teleports from your laptop screen over to the external monitor. When you look back at your laptop, the Dock is gone. This constant teleportation is highly disorienting and ruins your spatial memory of where your apps are located.
How to Lock the Dock to One Screen
The Dock moves because macOS treats every monitor as an independent workspace by default. To lock the Dock to your primary screen permanently, you must tell macOS that your monitors are part of one large, unified canvas.
1. Click the Apple logo () in the top-left corner of your menu bar.
2. Select System Settings (or System Preferences on older versions).
3. In the left-hand sidebar, click on Desktop & Dock (or “Mission Control” if you are on an older OS).
4. Scroll down until you find the section labelled “Mission Control.”
5. Locate the toggle switch labelled Displays have separate Spaces.
6. Turn this switch Off.
7. A prompt will appear stating that you must Log Out for the changes to take effect. Save your work, click Log Out, and log back in.
The Trade-off: Full-Screen Apps
By turning off “Displays have separate Spaces,” your Dock will now remain permanently locked to your primary monitor. However, this change alters how full-screen apps behave. If you maximize an application on your primary monitor, the secondary monitor will turn completely black, as the OS now considers both screens to be a single, massive display. If you frequently use full-screen apps on one monitor while watching YouTube on the other, you must re-enable “separate Spaces” and simply learn to tolerate the jumping Dock.