diff --git a/c/xlib/window.c b/c/xlib/window.c
index 1f315ff..9cecb92 100644
--- a/c/xlib/window.c
+++ b/c/xlib/window.c
@@ -74,7 +74,7 @@ s48_value scx_Create_Window (s48_value display, s48_value parent,
 		      (int)s48_extract_integer(height), 
 		      (int)s48_extract_integer(border_width),
 		      s48_extract_integer(depth),
-		      s48_extract_integer(class),
+		      scx_extract_window_class(class),
 		      scx_extract_visual(visual), mask, &Xattrs);
   S48_GC_RETURN(scx_enter_window(win));
 }