diff --git a/services/core/java/com/android/server/wm/Transition.java b/services/core/java/com/android/server/wm/Transition.java
index ded58f4..ad45948 100644
--- a/services/core/java/com/android/server/wm/Transition.java
+++ b/services/core/java/com/android/server/wm/Transition.java
@@ -1039,6 +1039,8 @@
                         "  Rejecting as detached: %s", wc);
                 continue;
             }
+            // The level of transition target should be at least window token.
+            if (wc.asWindowState() != null) continue;
 
             final ChangeInfo changeInfo = changes.get(wc);