diff --git a/sys/src/libdraw/window.c b/sys/src/libdraw/window.c
index 7f15b336f..d36b132bd 100644
--- a/sys/src/libdraw/window.c
+++ b/sys/src/libdraw/window.c
@@ -29,7 +29,7 @@ allocscreen(Image *image, Image *fill, int public)
 		a = bufimage(d, 1+4+4+4+1);
 		if(a == 0)
 			break;
-		id = ++screenid & 0xfffff;	/* old devdraw bug */
+		id = ++screenid & 0xffff;	/* old devdraw bug */
 		a[0] = 'A';
 		BPLONG(a+1, id);
 		BPLONG(a+5, image->id);