diff --git a/MatterControl.MeshOperations/CsgBySlicing.cs b/MatterControl.MeshOperations/CsgBySlicing.cs
index cb350a3f8..0e3d2c0ef 100644
--- a/MatterControl.MeshOperations/CsgBySlicing.cs
+++ b/MatterControl.MeshOperations/CsgBySlicing.cs
@@ -99,7 +99,6 @@ namespace MatterHackers.PolygonMesh
 				var matrix = SliceLayer.GetTransformTo0Plane(plane);
 				transformTo0Planes[plane] = (matrix, matrix.Inverted);
 			}
-
 		}
 
 		public Mesh Calculate(CsgModes operation,
@@ -118,6 +117,11 @@ namespace MatterHackers.PolygonMesh
             {
                 var mesh1 = transformedMeshes[mesh1Index];
 
+                if (cancellationToken.IsCancellationRequested)
+                {
+                    return null;
+                }
+
                 for (int faceIndex = 0; faceIndex < mesh1.Faces.Count; faceIndex++)
                 {
                     var face = mesh1.Faces[faceIndex];
diff --git a/Submodules/agg-sharp b/Submodules/agg-sharp
index 66f77f1cd..6a55bf626 160000
--- a/Submodules/agg-sharp
+++ b/Submodules/agg-sharp
@@ -1 +1 @@
-Subproject commit 66f77f1cd52f85b7ac3ac6b8e711ad01f32519c5
+Subproject commit 6a55bf6267d1d178666d1fda16f97a5beaeb8f5b