diff --git a/doc/man/man5/slapd-mdb.5 b/doc/man/man5/slapd-mdb.5
index 85f7235b17..3cfc8f6d59 100644
--- a/doc/man/man5/slapd-mdb.5
+++ b/doc/man/man5/slapd-mdb.5
@@ -27,6 +27,7 @@ come before any subsequent "backend" or "database" lines.
 Specify a power of 2 for the maximum size of an index slot.
 The default is 16, yielding a maximum slot size of 2^16 or 65536.
 Once set, this option applies to every \fBmdb\fP database instance.
+The specified value must be in the range of 16-31.
 .LP
 
 These