diff --git a/include/callback.h b/include/callback.h
index 00a67457..065dd9b5 100644
--- a/include/callback.h
+++ b/include/callback.h
@@ -24,7 +24,7 @@
 typedef Bitu (*CallBack_Handler)(void);
 extern CallBack_Handler CallBack_Handlers[];
 
-enum { CB_RETF,CB_IRET };
+enum { CB_RETF,CB_IRET,CB_IRET_STI };
 
 #define CB_MAX 1024
 #define CB_SEG 0xC800