diff --git a/services/tests/wmtests/src/com/android/server/wm/WindowContainerThumbnailTest.java b/services/tests/wmtests/src/com/android/server/wm/WindowContainerThumbnailTest.java
index b8de3ca4ea1cd..ee210b6eeaee0 100644
--- a/services/tests/wmtests/src/com/android/server/wm/WindowContainerThumbnailTest.java
+++ b/services/tests/wmtests/src/com/android/server/wm/WindowContainerThumbnailTest.java
@@ -18,6 +18,7 @@ package com.android.server.wm;
 
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.mock;
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.when;
+import static org.mockito.ArgumentMatchers.any;
 
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
@@ -49,6 +50,7 @@ public class WindowContainerThumbnailTest extends WindowTestsBase {
                 GraphicBuffer.USAGE_SW_READ_RARELY | GraphicBuffer.USAGE_SW_WRITE_NEVER);
         final ActivityRecord mockAr = mock(ActivityRecord.class);
         when(mockAr.getPendingTransaction()).thenReturn(new StubTransaction());
+        when(mockAr.makeChildSurface(any())).thenReturn(new MockSurfaceControlBuilder());
         when(mockAr.makeSurface()).thenReturn(new MockSurfaceControlBuilder());
         return new WindowContainerThumbnail(new StubTransaction(), mockAr,
                 buffer, false, mock(Surface.class), mock(SurfaceAnimator.class));