diff --git a/sys/geom/mirror/g_mirror.h b/sys/geom/mirror/g_mirror.h
index 1db45bd274f5..22b3ff692d51 100644
--- a/sys/geom/mirror/g_mirror.h
+++ b/sys/geom/mirror/g_mirror.h
@@ -62,6 +62,8 @@
 #define	G_MIRROR_DISK_FLAG_HARDCODED		0x0000000000000010ULL
 #define	G_MIRROR_DISK_FLAG_BROKEN		0x0000000000000020ULL
 #define	G_MIRROR_DISK_FLAG_CANDELETE		0x0000000000000040ULL
+
+/* Per-disk flags which are recorded in on-disk metadata. */
 #define	G_MIRROR_DISK_FLAG_MASK		(G_MIRROR_DISK_FLAG_DIRTY |	\
 					 G_MIRROR_DISK_FLAG_SYNCHRONIZING | \
 					 G_MIRROR_DISK_FLAG_FORCE_SYNC | \
@@ -70,6 +72,8 @@
 
 #define	G_MIRROR_DEVICE_FLAG_NOAUTOSYNC	0x0000000000000001ULL
 #define	G_MIRROR_DEVICE_FLAG_NOFAILSYNC	0x0000000000000002ULL
+
+/* Mirror flags which are recorded in on-disk metadata. */
 #define	G_MIRROR_DEVICE_FLAG_MASK	(G_MIRROR_DEVICE_FLAG_NOAUTOSYNC | \
 					 G_MIRROR_DEVICE_FLAG_NOFAILSYNC)