diff --git a/services/core/java/com/android/server/pm/UserManagerInternal.java b/services/core/java/com/android/server/pm/UserManagerInternal.java
index 8dc94287688d1..cc58e5c2354f5 100644
--- a/services/core/java/com/android/server/pm/UserManagerInternal.java
+++ b/services/core/java/com/android/server/pm/UserManagerInternal.java
@@ -305,4 +305,10 @@ public abstract class UserManagerInternal {
      * for users that already existed on-disk from an older version of Android.
      */
     public abstract boolean shouldIgnorePrepareStorageErrors(int userId);
+
+    /**
+     * Returns the user id of the main user, or {@link android.os.UserHandle#USER_NULL} if there is
+     * no main user.
+     */
+    public abstract @UserIdInt int getMainUserId();
 }
diff --git a/services/core/java/com/android/server/pm/UserManagerService.java b/services/core/java/com/android/server/pm/UserManagerService.java
index 914c4726b264d..89a920ab604b6 100644
--- a/services/core/java/com/android/server/pm/UserManagerService.java
+++ b/services/core/java/com/android/server/pm/UserManagerService.java
@@ -6376,6 +6376,11 @@ public class UserManagerService extends IUserManager.Stub {
                 return userData != null && userData.getIgnorePrepareStorageErrors();
             }
         }
+
+        @Override
+        public @UserIdInt int getMainUserId() {
+            return UserHandle.USER_SYSTEM;
+        }
     }
 
     /**