Index: uspace/lib/c/include/io/pixelmap.h
===================================================================
--- uspace/lib/c/include/io/pixelmap.h	(revision 6d5e378b28e2c858f3813b5d4d57fa46f709d753)
+++ uspace/lib/c/include/io/pixelmap.h	(revision 48171fc4f90f30adbbe6e443e48ddd9fb7ffdcf4)
@@ -52,7 +52,11 @@
     sysarg_t y)
 {
-	size_t offset = y * pixelmap->width + x;
-	pixel_t *pixel = pixelmap->data + offset;
-	return pixel;
+	if (x < pixelmap->width && y < pixelmap->height) {
+		size_t offset = y * pixelmap->width + x;
+		pixel_t *pixel = pixelmap->data + offset;
+		return pixel;
+	} else {
+		return NULL;
+	}
 }