diff --git a/Assets/MRTK/Extensions/LostTrackingService/LostTrackingService.cs b/Assets/MRTK/Extensions/LostTrackingService/LostTrackingService.cs
index 80fb87c5ffe..1feaf3faa85 100644
--- a/Assets/MRTK/Extensions/LostTrackingService/LostTrackingService.cs
+++ b/Assets/MRTK/Extensions/LostTrackingService/LostTrackingService.cs
@@ -9,6 +9,10 @@
 #if ARFOUNDATION_PRESENT
 using System.Collections.Generic;
 using UnityEngine.XR.ARSubsystems;
+
+#if UNITY_2018
+using UnityEngine.Experimental;
+#endif // UNITY_2018
 #endif // ARFOUNDATION_PRESENT
 
 #if UNITY_WSA && !UNITY_2020_1_OR_NEWER