diff --git a/OpenRa.Game/GameRules/FieldLoader.cs b/OpenRa.Game/GameRules/FieldLoader.cs
index 55731a6445..f1034dc5f0 100755
--- a/OpenRa.Game/GameRules/FieldLoader.cs
+++ b/OpenRa.Game/GameRules/FieldLoader.cs
@@ -21,6 +21,8 @@ namespace OpenRa.Game.GameRules
 			foreach (var x in my.Nodes)
 			{
 				var field = self.GetType().GetField(x.Key.Trim());
+				if (field == null)
+					throw new NotImplementedException("Missing field `{0}` on `{1}`".F(x.Key.Trim(), self.GetType().Name));
 				field.SetValue(self, GetValue(field.FieldType, x.Value.Value.Trim()));
 			}
 		}
diff --git a/OpenRa.Game/Traits/Buildable.cs b/OpenRa.Game/Traits/Buildable.cs
index fb1f95dc52..ebff7ae4d1 100755
--- a/OpenRa.Game/Traits/Buildable.cs
+++ b/OpenRa.Game/Traits/Buildable.cs
@@ -5,6 +5,18 @@ using System.Text;
 
 namespace OpenRa.Game.Traits
 {
+	class BuildableInfo : ITraitInfo
+	{
+		public readonly int TechLevel = -1;
+		public readonly string Tab = null;
+		public readonly string[] Prerequisites = { };
+		public readonly Race[] Owner = { };
+		public readonly int Cost = 0;
+		public readonly string Description = "";
+		public readonly string LongDesc = "";
+		public object Create(Actor self) { return new Buildable(self); }
+	}
+
 	class Buildable
 	{
 		public Buildable( Actor self ) { }
diff --git a/OpenRa.Game/Traits/Mobile.cs b/OpenRa.Game/Traits/Mobile.cs
index 7645d36cab..3f753ac289 100644
--- a/OpenRa.Game/Traits/Mobile.cs
+++ b/OpenRa.Game/Traits/Mobile.cs
@@ -7,9 +7,9 @@ namespace OpenRa.Game.Traits
 {
 	class MobileInfo : ITraitInfo
 	{
-		public readonly int Sight;
-		public readonly int ROT;
-		public readonly int Speed;
+		public readonly int Sight = 0;
+		public readonly int ROT = 0;
+		public readonly int Speed = 0;
 		public object Create(Actor self) { return new Mobile(self); }
 	}