Index: src/Common/NetTopologySuite/GeometriesGraph/Index/SweepLineSegment.cs
===================================================================
diff -u -r8f6ae890fed8e8eae3a32f9c0498a10f82e0ddf9 -r5fc71a385897af92ccb092f2f969b5709afab85a
--- src/Common/NetTopologySuite/GeometriesGraph/Index/SweepLineSegment.cs	(.../SweepLineSegment.cs)	(revision 8f6ae890fed8e8eae3a32f9c0498a10f82e0ddf9)
+++ src/Common/NetTopologySuite/GeometriesGraph/Index/SweepLineSegment.cs	(.../SweepLineSegment.cs)	(revision 5fc71a385897af92ccb092f2f969b5709afab85a)
@@ -7,9 +7,9 @@
     /// </summary>
     public class SweepLineSegment
     {
-        private Edge edge;
-        private ICoordinate[] pts;
-        int ptIndex;
+        private readonly Edge edge;
+        private readonly ICoordinate[] pts;
+        private readonly int ptIndex;
 
         /// <summary>
         /// 
@@ -59,4 +59,4 @@
             si.AddIntersections(edge, ptIndex, ss.edge, ss.ptIndex);
         }
     }
-}
+}
\ No newline at end of file