diff --git a/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceWindowGainedFocusTest.java b/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceWindowGainedFocusTest.java
index cea65b5..9f46d0ba 100644
--- a/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceWindowGainedFocusTest.java
+++ b/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceWindowGainedFocusTest.java
@@ -198,7 +198,9 @@
 
     @Test
     public void startInputOrWindowGainedFocus_userNotRunning() throws RemoteException {
-        when(mMockUserManagerInternal.isUserRunning(anyInt())).thenReturn(false);
+        // Run blockingly on ServiceThread to avoid that interfering with our stubbing.
+        mServiceThread.getThreadHandler().runWithScissors(
+                () -> when(mMockUserManagerInternal.isUserRunning(anyInt())).thenReturn(false), 0);
 
         assertThat(
                         startInputOrWindowGainedFocus(