diff --git a/MagickCore/xwindow.c b/MagickCore/xwindow.c
index 1d49525..a58c684 100644
--- a/MagickCore/xwindow.c
+++ b/MagickCore/xwindow.c
@@ -4942,7 +4942,7 @@
/*
Select window by ID or name.
*/
- if (isdigit((unsigned char) *image_info->filename) != 0)
+ if (isdigit((int) ((unsigned char) *image_info->filename)) != 0)
target=XWindowByID(display,root,(Window)
strtol(image_info->filename,(char **) NULL,0));
if (target == (Window) NULL)
@@ -5295,7 +5295,7 @@
windows->group_leader.id=(Window) NULL;
if (resource_info->window_group != (char *) NULL)
{
- if (isdigit((unsigned char) *resource_info->window_group) != 0)
+ if (isdigit((int) ((unsigned char) *resource_info->window_group)) != 0)
windows->group_leader.id=XWindowByID(display,root_window,(Window)
strtol((char *) resource_info->window_group,(char **) NULL,0));
if (windows->group_leader.id == (Window) NULL)
@@ -8929,7 +8929,7 @@
/*
Search window hierarchy and identify any clients by name or ID.
*/
- if (isdigit((unsigned char) *window) != 0)
+ if (isdigit((int) ((unsigned char) *window)) != 0)
remote_window=XWindowByID(display,root_window,(Window)
strtol((char *) window,(char **) NULL,0));
if (remote_window == (Window) NULL)