diff --git a/man3/pthread_mutex_consistent.3 b/man3/pthread_mutex_consistent.3
index d2ce17ddf..83da6900e 100644
--- a/man3/pthread_mutex_consistent.3
+++ b/man3/pthread_mutex_consistent.3
@@ -67,6 +67,20 @@ The mutex is either not robust or it is not in a inconsistent state.
 was added to glibc in version 2.12.
 .SH CONFORMING TO
 POSIX.1-2008.
+.SH NOTES
+Before the addition of
+.BR pthread_mutex_consistent ()
+to POSIX,
+glibc defined the following equivalent nonstandard function if
+.BR _GNU_SOURCE
+was defined:
+.PP
+.nf
+.BI "int pthread_mutex_consistent(const pthread_mutex_t *" mutex );
+.fi
+.PP
+This GNU-specific API, which first appeared in glibc 2.4,
+is nowadays obsolete and should not be used in new programs.
 .SH SEE ALSO
 .ad l
 .nh