diff --git a/services/core/java/com/android/server/wm/WindowToken.java b/services/core/java/com/android/server/wm/WindowToken.java
index f3980342ec2e4..ccaa03ae8fd0f 100644
--- a/services/core/java/com/android/server/wm/WindowToken.java
+++ b/services/core/java/com/android/server/wm/WindowToken.java
@@ -16,6 +16,7 @@
 
 package com.android.server.wm;
 
+import static android.app.WindowConfiguration.WINDOWING_MODE_FULLSCREEN;
 import static android.view.WindowManager.LayoutParams.TYPE_DOCK_DIVIDER;
 import static android.view.WindowManager.LayoutParams.TYPE_NAVIGATION_BAR;
 
@@ -615,6 +616,12 @@ class WindowToken extends WindowContainer<WindowState> {
             getResolvedOverrideConfiguration().updateFrom(
                     mFixedRotationTransformState.mRotatedOverrideConfiguration);
         }
+        if (getTaskDisplayArea() == null) {
+            // We only defined behaviors of system windows in fullscreen mode, i.e. windows not
+            // contained in a task display area.
+            getResolvedOverrideConfiguration().windowConfiguration.setWindowingMode(
+                    WINDOWING_MODE_FULLSCREEN);
+        }
     }
 
     @Override