diff --git a/OpenRA.FileFormats/MiniYaml.cs b/OpenRA.FileFormats/MiniYaml.cs
index fd09ad4608..04d3a1b9f9 100755
--- a/OpenRA.FileFormats/MiniYaml.cs
+++ b/OpenRA.FileFormats/MiniYaml.cs
@@ -21,7 +21,8 @@ namespace OpenRA.FileFormats
 	{
 		public struct SourceLocation
 		{
-			public string Filename; public int Line;
+			public string Filename; public int Line;
+            public override string ToString() { return "{0}:{1}".F(Filename, Line); }
 		}
 
 		public SourceLocation Location;
@@ -52,7 +53,12 @@ namespace OpenRA.FileFormats
 		public MiniYamlNode( string k, string v, List<MiniYamlNode> n, SourceLocation loc )
 			: this( k, new MiniYaml( v, n ), loc )
 		{
-		}
+		}
+
+        public override string ToString()
+        {
+            return "{{YamlNode: {0} @ {1}}}".F(Key, Location);
+        }
 	}
 
 	public class MiniYaml
@@ -95,7 +101,7 @@ namespace OpenRA.FileFormats
 				var level = line.Length - t.Length;
 
 				if (levels.Count <= level)
-					throw new InvalidOperationException("Bad indent in miniyaml");
+					throw new YamlException("Bad indent in miniyaml");
 				while (levels.Count > level + 1)
 					levels.RemoveAt(levels.Count - 1);
 
@@ -169,9 +175,10 @@ namespace OpenRA.FileFormats
 
 			var aDict = a.ToDictionary( x => x.Key );
 			var bDict = b.ToDictionary( x => x.Key );
-			var keys = aDict.Keys.Union( bDict.Keys ).ToList();
-
-			var noInherit = keys.Where( x => x.Length > 0 && x[ 0 ] == '-' ).Select( x => x.Substring( 1 ) ).ToList();
+			var keys = aDict.Keys.Union( bDict.Keys ).ToList();
+
+            var noInherit = keys.Where(x => x.Length > 0 && x[0] == '-')
+                .ToDictionary(x => x.Substring(1), x => false);
 
 			foreach( var key in keys )
 			{
@@ -179,10 +186,11 @@ namespace OpenRA.FileFormats
 				aDict.TryGetValue( key, out aa );
 				bDict.TryGetValue( key, out bb );
 
-				if( noInherit.Contains( key ) )
+				if( noInherit.ContainsKey( key ) )
 				{
-					if( aa != null )
-						ret.Add( aa );
+			//		if( aa != null )
+			//			ret.Add( aa );
+                    noInherit[key] = true;
 				}
 				else
 				{
@@ -190,7 +198,11 @@ namespace OpenRA.FileFormats
 					var merged = ( aa == null || bb == null ) ? aa ?? bb : new MiniYamlNode( key, Merge( aa.Value, bb.Value ), loc );
 					ret.Add( merged );
 				}
-			}
+			}
+
+            if (noInherit.ContainsValue(false))
+                throw new YamlException("Bogus yaml removals: {0}".F(
+                    string.Join(", ", noInherit.Where(x => !x.Value).Select(x => x.Key).ToArray())));
 
 			return ret;
 		}
@@ -236,5 +248,10 @@ namespace OpenRA.FileFormats
 					yield return "";
 			}
 		}
-	}
+	}
+
+    public class YamlException : Exception
+    {
+        public YamlException(string s) : base(s) { }
+    }
 }
diff --git a/OpenRA.Game/GameRules/ActorInfo.cs b/OpenRA.Game/GameRules/ActorInfo.cs
index 39c0065c18..f421c34138 100644
--- a/OpenRA.Game/GameRules/ActorInfo.cs
+++ b/OpenRA.Game/GameRules/ActorInfo.cs
@@ -22,14 +22,30 @@ namespace OpenRA
 		public readonly TypeDictionary Traits = new TypeDictionary();
 
 		public ActorInfo( string name, MiniYaml node, Dictionary<string, MiniYaml> allUnits )
-		{
-			var mergedNode = MergeWithParent( node, allUnits ).NodesDict;
-
-			Name = name;
-			foreach( var t in mergedNode )
-				if( t.Key != "Inherits" && !t.Key.StartsWith("-") )
-					Traits.Add( LoadTraitInfo( t.Key.Split('@')[0], t.Value ) );
-		}
+		{
+            try
+            {
+                var mergedNode = MergeWithParent(node, allUnits).NodesDict;
+
+                Name = name;
+                foreach (var t in mergedNode)
+                    if (t.Key != "Inherits" && !t.Key.StartsWith("-"))
+                        Traits.Add(LoadTraitInfo(t.Key.Split('@')[0], t.Value));
+            }
+            catch (YamlException e)
+            {
+                throw new YamlException("Actor type {0}: {1}".F(name, e.Message));
+            }
+		}
+
+        static IEnumerable<MiniYaml> GetInheritanceChain(MiniYaml node, Dictionary<string, MiniYaml> allUnits)
+        {
+            while (node != null)
+            {
+                yield return node;
+                node = GetParent(node, allUnits);
+            }
+        }
 
 		static MiniYaml GetParent( MiniYaml node, Dictionary<string, MiniYaml> allUnits )
 		{
@@ -49,9 +65,15 @@ namespace OpenRA
 
 		static MiniYaml MergeWithParent( MiniYaml node, Dictionary<string, MiniYaml> allUnits )
 		{
-			var parent = GetParent( node, allUnits );
-			if( parent != null )
-				return MiniYaml.Merge( node, MergeWithParent( parent, allUnits ) );
+			var parent = GetParent( node, allUnits );
+            if (parent != null)
+            {
+                var result = MiniYaml.Merge(node, MergeWithParent(parent, allUnits));
+
+                // strip the '-'
+                result.Nodes.RemoveAll(a => a.Key.StartsWith("-"));
+                return result;
+            }
 			return node;
 		}