diff --git a/doc/install.texi b/doc/install.texi
index 761be0ba0..8756bca76 100644
--- a/doc/install.texi
+++ b/doc/install.texi
@@ -98,4 +98,9 @@ On Irix there are three different ABIs that can be used (@samp{32},
 @samp{n32}, or @samp{64}).  This option allows you to override the
 automatic selection.
 
+@item @kbd{--disable-mmap}
+Do not use the mmap system call.  Normally, configure detects if there
+is a working mmap and it is only used if there is one.  Only try this
+option if it fails to work anyhow.
+
 @end table