diff --git a/OpenRA.Game/Traits/World/ResourceType.cs b/OpenRA.Game/Traits/World/ResourceType.cs
index 79a1e25e92..d2cec0017a 100644
--- a/OpenRA.Game/Traits/World/ResourceType.cs
+++ b/OpenRA.Game/Traits/World/ResourceType.cs
@@ -1,4 +1,4 @@
-#region Copyright & License Information
+#region Copyright & License Information
 /*
  * Copyright 2007,2009,2010 Chris Forbes, Robert Pepperell, Matthew Bowra-Dean, Paul Chote, Alli Witheford.
  * This file is part of OpenRA.
@@ -24,7 +24,7 @@ namespace OpenRA.Traits
 {
 	public class ResourceTypeInfo : ITraitInfo
 	{
-		public readonly int[] Overlays = { };
+		public readonly string[] Overlays = { };
 		public readonly string[] SpriteNames = { };
 		public readonly string Palette = "terrain";
 
diff --git a/OpenRA.Game/Traits/World/WallLoadHook.cs b/OpenRA.Game/Traits/World/WallLoadHook.cs
index 806179183e..0d6aaa8c3a 100644
--- a/OpenRA.Game/Traits/World/WallLoadHook.cs
+++ b/OpenRA.Game/Traits/World/WallLoadHook.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
@@ -7,7 +7,7 @@ namespace OpenRA.Traits
 {
 	class WallLoadHookInfo : ITraitInfo
 	{
-		public readonly int[] OverlayIndices = { };
+		public readonly string[] OverlayTypes = { };
 		public readonly string ActorType = "brik";
 
 		public object Create(Actor self) { return new WallLoadHook( self, this ); }
@@ -27,7 +27,7 @@ namespace OpenRA.Traits
 
 			for (int y = map.YOffset; y < map.YOffset + map.Height; y++)
 				for (int x = map.XOffset; x < map.XOffset + map.Width; x++)
-					if (info.OverlayIndices.Contains(w.Map.MapTiles[x, y].overlay))
+					if (info.OverlayTypes.Contains(w.Map.MapTiles[x, y].overlay))
 						w.CreateActor(info.ActorType, new int2(x, y), w.players[0]);	// todo: neutral player or null?
 		}
 	}
diff --git a/mods/ra/rules.yaml b/mods/ra/rules.yaml
index b61de4ae82..6be0b8fb5e 100644
--- a/mods/ra/rules.yaml
+++ b/mods/ra/rules.yaml
@@ -213,25 +213,25 @@ World:
 	PowerDownButton:
 	WallLoadHook@sbag:
 		ActorType: sbag
-		OverlayIndices: 0,24
+		OverlayTypes: sbag
 	WallLoadHook@cycl:
 		ActorType: cycl
-		OverlayIndices: 1
+		OverlayTypes: cycl
 	WallLoadHook@brik:
 		ActorType: brik
-		OverlayIndices: 2
+		OverlayTypes: brik
 	WallLoadHook@fenc:
 		ActorType: fenc
-		OverlayIndices: 3
+		OverlayTypes: fenc
 	WallLoadHook@wood:
 		ActorType: wood
-		OverlayIndices: 4
+		OverlayTypes: wood
 	WallLoadHook@barb:
 		ActorType: barb
-		OverlayIndices: 23
+		OverlayTypes: barb
 	ResourceLayer:
 	ResourceType@ore:
-		Overlays: 5,6,7,8
+		Overlays: gold01,gold02,gold03,gold04
 		Palette: terrain
 		SpriteNames: gold01,gold02,gold03,gold04
 		ValuePerUnit: 25
@@ -239,7 +239,7 @@ World:
 		GrowthInterval: .3
 		SpreadInterval: .7
 	ResourceType@gem:
-		Overlays: 9,10,11,12
+		Overlays: gem01,gem02,gem03,gem04
 		Palette: terrain
 		SpriteNames: gem01,gem02,gem03,gem04
 		ValuePerUnit: 50