Submitted upstream at https://github.com/weechat/weechat/pull/1163

diff -u -r ../weechat-2.1/src/gui/curses/headless/main.c ./src/gui/curses/headless/main.c
--- ../weechat-2.1/src/gui/curses/headless/main.c	2018-03-18 07:41:40.000000000 +0100
+++ ./src/gui/curses/headless/main.c	2018-03-18 21:08:49.664939605 +0100
@@ -72,7 +72,7 @@
     setsid ();
 
     /* close all file descriptors */
-    for (i = getdtablesize(); i >= 0; --i)
+    for (i = sysconf(_SC_OPEN_MAX); i >= 0; --i)
     {
         close (i);
     }