diff --git a/wand/mogrify.c b/wand/mogrify.c
index bf8077b..d162564 100644
--- a/wand/mogrify.c
+++ b/wand/mogrify.c
@@ -6733,7 +6733,7 @@
             if (*option == '+')
               {
                 image_info->dither=MagickFalse;
-                (void) SetImageOption(image_info,option+1,"undefined");
+                (void) SetImageOption(image_info,option+1,"none");
                 break;
               }
             (void) SetImageOption(image_info,option+1,argv[i+1]);