diff --git a/services/core/java/com/android/server/wm/DisplayContent.java b/services/core/java/com/android/server/wm/DisplayContent.java
index 5d6df26..4db0b1e 100644
--- a/services/core/java/com/android/server/wm/DisplayContent.java
+++ b/services/core/java/com/android/server/wm/DisplayContent.java
@@ -203,7 +203,9 @@
     }
 
     void moveStack(TaskStack stack, boolean toTop) {
-        mStacks.remove(stack);
+        if (!mStacks.remove(stack)) {
+            Slog.wtf(TAG, "moving stack that was not added: " + stack, new Throwable());
+        }
         mStacks.add(toTop ? mStacks.size() : 0, stack);
     }