diff --git a/os/layers/contestant/includes.chroot/usr/share/gnome-shell/extensions/contest-lock@soi.ch/extension.js b/os/layers/contestant/includes.chroot/usr/share/gnome-shell/extensions/contest-lock@soi.ch/extension.js
index d73ab3a..92c3d37 100644
--- a/os/layers/contestant/includes.chroot/usr/share/gnome-shell/extensions/contest-lock@soi.ch/extension.js
+++ b/os/layers/contestant/includes.chroot/usr/share/gnome-shell/extensions/contest-lock@soi.ch/extension.js
@@ -10,6 +10,7 @@ const {
 const Background = imports.ui.background;
 const Layout = imports.ui.layout;
 const Main = imports.ui.main;
+const ScreenShield = imports.ui.screenShield;
 
 // half of the time for which a frame is displayed
 const HALF_FRAME_TIME_MS = 8;
@@ -254,6 +255,14 @@ function activate () {
     return;
   }
 
+  // Monkeypatch disable regular lock screen deactivation.
+  // It is possible to trigger this function while contest lock is active,
+  // by pressing Ctrl+Alt+F1. This switches to GDM, which, after the automatic
+  // login timeout, switches back to our session and emits an Unlock signal.
+  // If we did not disable it here, this would then partially unlock the screen,
+  // such that you can interact with the Gnome Shell but not with applications.
+  ScreenShield.ScreenShield.prototype.deactivate = () => {};
+
   actor.show();
 
   Main.sessionMode.pushMode('unlock-dialog');