diff --git a/sys/sys/memrange.h b/sys/sys/memrange.h
index 36e354df49c7..bd18f590b467 100644
--- a/sys/sys/memrange.h
+++ b/sys/sys/memrange.h
@@ -10,6 +10,7 @@
 #define MDF_WRITETHROUGH	(1<<2)	/* write-through cached */
 #define MDF_WRITEBACK		(1<<3)	/* write-back cached */
 #define MDF_WRITEPROTECT	(1<<4)	/* read-only region */
+#define MDF_UNKNOWN		(1<<5)	/* any state we don't understand */
 #define MDF_ATTRMASK		(0x00ffffff)
 
 #define MDF_FIXBASE		(1<<24)	/* fixed base */
diff --git a/usr.sbin/memcontrol/memcontrol.c b/usr.sbin/memcontrol/memcontrol.c
index 88d4768f6814..2554723733a9 100644
--- a/usr.sbin/memcontrol/memcontrol.c
+++ b/usr.sbin/memcontrol/memcontrol.c
@@ -50,6 +50,7 @@ struct
     {"write-through",	MDF_WRITETHROUGH,	MDF_SETTABLE},
     {"write-back",	MDF_WRITEBACK,		MDF_SETTABLE},
     {"write-protect",	MDF_WRITEPROTECT,	MDF_SETTABLE},
+    {"unknown",		MDF_UNKNOWN,		0},
     {"fixed-base",	MDF_FIXBASE,		0},
     {"fixed-length",	MDF_FIXLEN,		0},
     {"set-by-firmware",	MDF_FIRMWARE,		0},