1 files changed, 11 insertions, 4 deletions

diff --git a/doc/ref/posix.texi b/doc/ref/posix.texi
index 64e668d17..5cb68a292 100644
--- a/doc/ref/posix.texi
+++ b/doc/ref/posix.texi
@@ -1,7 +1,7 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
 @c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007,
-@c   2008, 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.
+@c   2008, 2009, 2010, 2011, 2012, 2013, 2014, 2017 Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
 @node POSIX
@@ -2162,12 +2162,12 @@ expiry will be signalled.
 A real-time timer, counting down elapsed real time.  At zero it raises
 @code{SIGALRM}.  This is like @code{alarm} above, but with a higher
 resolution period.
-@end defvar 
+@end defvar
 
 @defvar ITIMER_VIRTUAL
 A virtual-time timer, counting down while the current process is
 actually using CPU.  At zero it raises @code{SIGVTALRM}.
-@end defvar 
+@end defvar
 
 @defvar ITIMER_PROF
 A profiling timer, counting down while the process is running (like
@@ -2176,7 +2176,7 @@ process's behalf.  At zero it raises a @code{SIGPROF}.
 
 This timer is intended for profiling where a program is spending its
 time (by looking where it is when the timer goes off).
-@end defvar 
+@end defvar
 
 @code{getitimer} returns the restart timer value and its current value,
 as a list containing two pairs.  Each pair is a time in seconds and
@@ -2196,6 +2196,13 @@ previous setting, in the same form as @code{getitimer} returns.
 
 Although the timers are programmed in microseconds, the actual
 accuracy might not be that high.
+
+Note that @code{ITIMER_PROF} and @code{ITIMER_VIRTUAL} are not
+functional on all platforms and may always error when called.
+@code{(provided? 'ITIMER_PROF)} and @code{(provided? 'ITIMER_VIRTUAL)}
+can be used to test if the those itimers are supported on the given
+host.  @code{ITIMER_REAL} is supported on all platforms that support
+@code{setitimer}.
 @end deffn