diff --git a/man5/nsswitch.conf.5 b/man5/nsswitch.conf.5
index 1e0ec3ce9..7a5b744ad 100644
--- a/man5/nsswitch.conf.5
+++ b/man5/nsswitch.conf.5
@@ -28,7 +28,7 @@ nsswitch.conf \- Name Service Switch configuration file
 .SH DESCRIPTION
 The Name Service Switch (NSS) configuration file,
 .IR /etc/nsswitch.conf ,
-is used by the GNU C Library to determine
+is used by the GNU C Library and certain other applications to determine
 the sources from which to obtain name-service information in
 a range of categories,
 and in what order.
@@ -102,6 +102,14 @@ Shadow user passwords, used by
 .BR getspnam (3)
 and related functions.
 .LP
+The GNU C Library ignores databases with unknown names.  Some
+applications use this to implement special handling for their own
+databases.  For example,
+.BR sudo (8)
+consults the
+.B sudoers
+database.
+.LP
 Here is an example
 .I /etc/nsswitch.conf
 file: