diff --git a/magick/quantum-private.h b/magick/quantum-private.h
index ec8cae2..c9322fa 100644
--- a/magick/quantum-private.h
+++ b/magick/quantum-private.h
@@ -564,7 +564,7 @@
 {
   if (quantum <= 0.0)
     return(0);
-  if ((quantum/65537.0) >= 65535.0)
+  if ((quantum/281479271743489.0) >= 65535.0)
     return(65535);
   return((unsigned short) (quantum/281479271743489.0+0.5));
 }