diff --git a/src/syscalls/ffi-functions-unix.lisp b/src/syscalls/ffi-functions-unix.lisp
index 9f8a7bf92f0c1b6287597ce88f82dfc65f7bcecf..dd8bdba800919e41e0d8479cf7e8255036aa2489 100644
--- a/src/syscalls/ffi-functions-unix.lisp
+++ b/src/syscalls/ffi-functions-unix.lisp
@@ -477,6 +477,10 @@ Return two values: the file descriptor and the path of the temporary file."
 
 (defsyscall (fd-open-p "lfp_is_fd_open") bool-designator
   (fd :int))
+
+(defsyscall (fd-tty-p "isatty") bool-designator
+  (fd :int))
+
 
 
 ;;;-------------------------------------------------------------------------
diff --git a/src/syscalls/pkgdcl.lisp b/src/syscalls/pkgdcl.lisp
index 16a145f5af52bac34273a4139bbb8116ab1cfa7a..9ba3297bbfd398bcf7da604ae0ef552cf7f3304e 100644
--- a/src/syscalls/pkgdcl.lisp
+++ b/src/syscalls/pkgdcl.lisp
@@ -523,7 +523,8 @@
    #:ioctl
    #:fd-cloexec-p
    #:fd-nonblock-p
-   #:fd-open-p)
+   #:fd-open-p
+   #:fd-tty-p)
   (:export ;; TTYs
    #:openpt
    #:grantpt