diff --git a/src/option.h b/src/option.h
index 2a4ffba..6ab1989 100644
--- a/src/option.h
+++ b/src/option.h
@@ -911,11 +911,13 @@
 EXTERN char_u	*p_sws;		// 'swapsync'
 EXTERN char_u	*p_swb;		// 'switchbuf'
 EXTERN unsigned	swb_flags;
+// Keep in sync with p_swb_values in optionstr.c
 #define SWB_USEOPEN		0x001
 #define SWB_USETAB		0x002
 #define SWB_SPLIT		0x004
 #define SWB_NEWTAB		0x008
 #define SWB_VSPLIT		0x010
+#define SWB_USELAST		0x020
 EXTERN char_u	*p_syn;		// 'syntax'
 EXTERN long	p_ts;		// 'tabstop'
 EXTERN int	p_tbs;		// 'tagbsearch'