diff --git a/Source/Engine/Terrain/Terrain.h b/Source/Engine/Terrain/Terrain.h
index dd9dc1926..b5bf0ae5c 100644
--- a/Source/Engine/Terrain/Terrain.h
+++ b/Source/Engine/Terrain/Terrain.h
@@ -10,6 +10,7 @@ class Terrain;
 class TerrainChunk;
 class TerrainPatch;
 class TerrainManager;
+class PhysicalMaterial;
 struct RayCastHit;
 struct RenderView;