--- ImageMagick-5.5.6/coders/xwd.c.mask	2003-01-04 22:55:30.000000000 -0500
+++ ImageMagick-5.5.6/coders/xwd.c	2005-05-26 08:22:43.627646000 -0400
@@ -343,21 +343,21 @@
         */
         red_mask=ximage->red_mask;
         red_shift=0;
-        while ((red_mask & 0x01) == 0)
+        while ((red_mask != 0) && ((red_mask & 0x01) == 0))
         {
           red_mask>>=1;
           red_shift++;
         }
         green_mask=ximage->green_mask;
         green_shift=0;
-        while ((green_mask & 0x01) == 0)
+        while ((green_mask != 0) && ((green_mask & 0x01) == 0))
         {
           green_mask>>=1;
           green_shift++;
         }
         blue_mask=ximage->blue_mask;
         blue_shift=0;
-        while ((blue_mask & 0x01) == 0)
+        while ((blue_mask != 0) && ((blue_mask & 0x01) == 0))
         {
           blue_mask>>=1;
           blue_shift++;