diff --git a/services/core/java/com/android/server/wm/ActivityTaskManagerService.java b/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
index 14df505..014b682 100644
--- a/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
+++ b/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
@@ -54,6 +54,7 @@
 import static android.os.Process.SYSTEM_UID;
 import static android.os.Trace.TRACE_TAG_WINDOW_MANAGER;
 import static android.provider.Settings.Global.DEVELOPMENT_ENABLE_FREEFORM_WINDOWS_SUPPORT;
+import static android.provider.Settings.Global.DEVELOPMENT_ENABLE_SIZECOMPAT_FREEFORM;
 import static android.provider.Settings.Global.DEVELOPMENT_FORCE_RESIZABLE_ACTIVITIES;
 import static android.provider.Settings.Global.DEVELOPMENT_FORCE_RTL;
 import static android.provider.Settings.Global.HIDE_ERROR_DIALOGS;
@@ -569,6 +570,7 @@
     boolean mSupportsPictureInPicture;
     boolean mSupportsMultiDisplay;
     boolean mForceResizableActivities;
+    boolean mSizeCompatFreeform;
 
     final List<ActivityTaskManagerInternal.ScreenObserver> mScreenObservers = new ArrayList<>();
 
@@ -744,6 +746,8 @@
         final boolean forceRtl = Settings.Global.getInt(resolver, DEVELOPMENT_FORCE_RTL, 0) != 0;
         final boolean forceResizable = Settings.Global.getInt(
                 resolver, DEVELOPMENT_FORCE_RESIZABLE_ACTIVITIES, 0) != 0;
+        final boolean sizeCompatFreeform = Settings.Global.getInt(
+                resolver, DEVELOPMENT_ENABLE_SIZECOMPAT_FREEFORM, 0) != 0;
 
         // Transfer any global setting for forcing RTL layout, into a System Property
         DisplayProperties.debug_force_rtl(forceRtl);
@@ -757,6 +761,7 @@
 
         synchronized (mGlobalLock) {
             mForceResizableActivities = forceResizable;
+            mSizeCompatFreeform = sizeCompatFreeform;
             final boolean multiWindowFormEnabled = freeformWindowManagement
                     || supportsSplitScreenMultiWindow
                     || supportsPictureInPicture
@@ -3393,6 +3398,9 @@
 
                 if (stack.inFreeformWindowingMode()) {
                     stack.setWindowingMode(WINDOWING_MODE_FULLSCREEN);
+                } else if (!mSizeCompatFreeform) {
+                    throw new IllegalStateException("Size-compat windows are currently not"
+                            + "freeform-enabled");
                 } else if (stack.getParent().inFreeformWindowingMode()) {
                     // If the window is on a freeform display, set it to undefined. It will be
                     // resolved to freeform and it can adjust windowing mode when the display mode