diff --git a/OpenRA.FileFormats/ConnectedComponents.cs b/OpenRA.FileFormats/ConnectedComponents.cs
index a1216cdb86..de43f975f3 100644
--- a/OpenRA.FileFormats/ConnectedComponents.cs
+++ b/OpenRA.FileFormats/ConnectedComponents.cs
@@ -14,7 +14,7 @@ namespace OpenRA.FileFormats
 		{
 			var result = new int[m.MapSize, m.MapSize];
 			var types = new int[m.MapSize, m.MapSize];
-			var d = new Dictionary<int,int>();
+			var d = new Dictionary<int, Node>();
 			var n = 1;
 
 			for( var j = m.YOffset; j < m.YOffset + m.Height; j++ )
@@ -23,14 +23,57 @@ namespace OpenRA.FileFormats
 					types[i, j] = f(i, j);
 
 					var k = n;
-					foreach (var a in Neighbors)
-						if (types[i + a.X, j + a.Y] == types[i, j] && result[i + a.X, j + a.Y] < k)
-							k = result[i + a.X, j + a.Y];
 
-					// todo: finish this
+					foreach (var a in Neighbors)
+						if (types[i + a.X, j + a.Y] == types[i, j])
+							k = (k == n) 
+								? result[i + a.X, j + a.Y]
+								: Union( d, k, result[i+a.X, j+a.Y] );
+
+					result[i,j] = k;
+					if (k == n) MakeSet(d, n++);
 				}
 
+			for (var j = m.YOffset; j < m.YOffset + m.Height; j++)
+				for (var i = m.XOffset; i < m.XOffset + m.Width; i++)
+					result[i, j] = Find(d, result[i, j]);
+
 			return result;
 		}
+
+		// disjoint-set forest stuff
+
+		class Node { public int a, b; public Node(int a, int b) { this.a = a; this.b = b; } }
+
+		static int MakeSet(Dictionary<int, Node> d, int x)
+		{
+			d[x] = new Node(x, 0);
+			return x;
+		}
+
+		static int Union(Dictionary<int, Node> d, int x, int y)
+		{
+			var xr = Find(d, x);
+			var yr = Find(d, y);
+			var xa = d[xr].b;
+			var ya = d[yr].b;
+
+			if (xa > ya) d[yr].a = xr;
+			else if (xa < ya) d[xr].a = yr;
+			else if (xr != yr)
+			{
+				d[yr].a = xr;
+				++d[xr].b;
+			}
+
+			return xr;
+		}
+
+		static int Find(Dictionary<int, Node> d, int x)
+		{
+			if (d[x].a == x) return x;
+			return d[x].a = Find(d, d[x].a);
+		}
+
 	}
 }