diff --git a/config-daemon.ac b/config-daemon.ac
index a13525a7f5..072fb84b46 100644
--- a/config-daemon.ac
+++ b/config-daemon.ac
@@ -78,10 +78,13 @@ if test "x$guix_build_daemon" = "xyes"; then
   dnl lutimes and lchown: used when canonicalizing store items.
   dnl posix_fallocate: used when extracting archives.
   dnl vfork: to speed up spawning of helper programs.
+  dnl   `--> now disabled because of unpredictable behavior:
+  dnl        see <http://lists.gnu.org/archive/html/guix-devel/2014-05/msg00036.html>
+  dnl        and Nix commit f794465c (Nov. 2012).
   dnl sched_setaffinity: to improve RPC locality.
   dnl statvfs: to detect disk-full conditions.
   dnl strsignal: for error reporting.
-  AC_CHECK_FUNCS([lutimes lchown posix_fallocate vfork sched_setaffinity \
+  AC_CHECK_FUNCS([lutimes lchown posix_fallocate sched_setaffinity \
      statvfs nanosleep strsignal])
 
   dnl Check whether the store optimiser can optimise symlinks.