diff --git a/MagickCore/channel.c b/MagickCore/channel.c
index 40c8aa6..723cd9d 100644
--- a/MagickCore/channel.c
+++ b/MagickCore/channel.c
@@ -329,7 +329,7 @@
     {
       case AssignChannelOp:
       {
-        pixel=StringToDouble(token,(char **) NULL);
+        pixel=StringToDoubleInterval(token,(double) QuantumRange+1.0);
         GetMagickToken(p,&p,token);
         break;
       }