diff --git a/ChangeLog b/ChangeLog
index 8b5050be4d..8851c6be85 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2015-09-29  Carlos O'Donell  <carlos@redhat.com>
+
+	* manual/filesys.texi (Storage Allocation): Document that
+	posix_fallocate emulation fails when fd is open with O_WRONLY.
+
 2015-09-28  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #19016]
diff --git a/manual/filesys.texi b/manual/filesys.texi
index ed4f5fdd85..40648853bd 100644
--- a/manual/filesys.texi
+++ b/manual/filesys.texi
@@ -3299,6 +3299,10 @@ There is a race condition if another thread or process modifies the
 underlying file in the to-be-allocated area.  Non-null bytes could be
 overwritten with null bytes.
 
+@item
+If @var{fd} has been opened with the @code{O_WRONLY} flag, the function
+will fail with an @code{errno} value of @code{EBADF}.
+
 @item
 If @var{fd} has been opened with the @code{O_APPEND} flag, the function
 will fail with an @code{errno} value of @code{EBADF}.