diff --git a/Source/Plugins/3DFloorMode/ThreeDFloor.cs b/Source/Plugins/3DFloorMode/ThreeDFloor.cs
index 9380beba..c102c5ed 100644
--- a/Source/Plugins/3DFloorMode/ThreeDFloor.cs
+++ b/Source/Plugins/3DFloorMode/ThreeDFloor.cs
@@ -225,10 +225,10 @@ namespace CodeImp.DoomBuilder.ThreeDFloorMode
 				sd.SetTextureMid(bordertexture);
 
 				if (sd.Line.Action == 160)
-				{					
-					sd.Line.Args[1] = type;
-					sd.Line.Args[2] = flags;
-					sd.Line.Args[3] = alpha;
+				{
+					// We need to update the linedef's args, but we can't do it directly because otherwise their state will not be saved for the undo snapshot,
+					// so we're using the linedef's update method
+					sd.Line.Update(sd.Line.GetFlags(), sd.Line.Activate, sd.Line.Tags, sd.Line.Action, new int[] { sd.Line.Args[0], type, flags, alpha, sd.Line.Args[4] });
 				}
 			}
 		}