diff --git a/wmtime/wmtime-mask.xbm b/wmtime/wmtime-mask.xbm
index dd73c69..cf3b1ca 100644
--- a/wmtime/wmtime-mask.xbm
+++ b/wmtime/wmtime-mask.xbm
@@ -1,6 +1,6 @@
 #define wmtime_mask_width 128
 #define wmtime_mask_height 64
-static char wmtime_mask_bits[] = {
+static unsigned char wmtime_mask_bits[] = {
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
diff --git a/wmtime/wmtime.c b/wmtime/wmtime.c
index 14a0544..75c885c 100644
--- a/wmtime/wmtime.c
+++ b/wmtime/wmtime.c
@@ -350,7 +350,7 @@ void wmtime_routine(int argc, char **argv) {
 	}
 
 draw_window:
-	openXwindow(argc, argv, wmtime_master_xpm, wmtime_mask_bits, 128, 64);
+	openXwindow(argc, argv, wmtime_master_xpm, (char*)wmtime_mask_bits, 128, 64);
 
 	/* Mask out the right parts of the clock */
 	copyXPMArea(0, 0, 128, 64, 0, 98);   /* Draw the borders */