diff --git a/sbin/fsck_ffs/fsck_ffs.8 b/sbin/fsck_ffs/fsck_ffs.8
index c85b94a789e6..a64c7ce8b5e7 100644
--- a/sbin/fsck_ffs/fsck_ffs.8
+++ b/sbin/fsck_ffs/fsck_ffs.8
@@ -173,8 +173,8 @@ exits without attempting any further cleaning.
 .It Fl b
 Use the block specified immediately after the flag as
 the super block for the file system.
-Block 32 is usually
-an alternate super block.
+An alternate super block is usually located at block 32 for UFS1,
+and block 160 for UFS2.
 .It Fl c
 Convert the file system to the specified level.
 Note that the level of a file system can only be raised.