diff --git a/MagickCore/xwindow.c b/MagickCore/xwindow.c
index fb3c224..7584f3a 100644
--- a/MagickCore/xwindow.c
+++ b/MagickCore/xwindow.c
@@ -7701,7 +7701,7 @@
   double
     intensity;
 
-  intensity=0.298839*pixel->red+0.586811*pixel->green+0.114350*pixel->blue;
+  intensity=0.298839f*pixel->red+0.586811f*pixel->green+0.114350f*pixel->blue;
   return(intensity);
 }