diff --git a/man7/sem_overview.7 b/man7/sem_overview.7
index d2c6c2762..ef354feca 100644
--- a/man7/sem_overview.7
+++ b/man7/sem_overview.7
@@ -23,7 +23,7 @@
 .\" Formatted or processed versions of this manual, if unaccompanied by
 .\" the source, must acknowledge the copyright and authors of this work.
 .\"
-.TH SEM_OVERVIEW 7 2009-02-20 "Linux" "Linux Programmer's Manual"
+.TH SEM_OVERVIEW 7 2009-02-25 "Linux" "Linux Programmer's Manual"
 .SH NAME
 sem_overview \- Overview of POSIX semaphores
 .SH DESCRIPTION
@@ -46,8 +46,8 @@ unnamed semaphores.
 A named semaphore is identified by a name of the form
 .IR /somename ;
 that is, a null-terminated string of up to
-.BI NAME_MAX +1
-(i.e., 256) characters consisting of an initial slash,
+.BI NAME_MAX \-4
+(i.e., 251) characters consisting of an initial slash,
 .\" glibc allows the initial slash to be omitted, and makes
 .\" multiple initial slashes equivalent to a single slash.
 .\" This differs from the implementation of POSIX message queues.
@@ -127,6 +127,11 @@ normally mounted under
 .IR /dev/shm ,
 with names of the form
 .IR \fBsem.\fPsomename .
+(This is the reason that semaphore names are limited to
+.BI NAME_MAX \-4
+rather than
+.B NAME_MAX
+characters.)
 
 Since Linux 2.6.19, ACLs can be placed on files under this directory,
 to control object permissions on a per-user and per-group basis.