diff --git a/programs/KOSfuncs.inc b/programs/KOSfuncs.inc
index 530318d0c..089443ae1 100644
--- a/programs/KOSfuncs.inc
+++ b/programs/KOSfuncs.inc
@@ -106,6 +106,7 @@ SF_MOUSE_GET=37
   SSF_SCROLL_DATA=7
 SF_DRAW_LINE=38
 SF_BACKGROUND_GET=39
+  SSF_RECT_BG=3         ; get rect from the background image
 SF_SET_EVENTS_MASK=40   ; turn on/off desired events
 SF_SET_PORTS=46         ; reserve/free a group of input/output ports
 SF_DRAW_NUMBER=47       ; draw number to the window