diff --git a/tests/gpgscm/ffi.c b/tests/gpgscm/ffi.c
index add82f700..c91d4aabe 100644
--- a/tests/gpgscm/ffi.c
+++ b/tests/gpgscm/ffi.c
@@ -325,6 +325,21 @@ do_close (scheme *sc, pointer args)
   FFI_RETURN_ERR (sc, close (fd) == 0 ? 0 : gpg_error_from_syserror ());
 }
 
+static pointer
+do_seek (scheme *sc, pointer args)
+{
+  FFI_PROLOG ();
+  int fd;
+  off_t offset;
+  int whence;
+  FFI_ARG_OR_RETURN (sc, int, fd, number, args);
+  FFI_ARG_OR_RETURN (sc, off_t, offset, number, args);
+  FFI_ARG_OR_RETURN (sc, int, whence, number, args);
+  FFI_ARGS_DONE_OR_RETURN (sc, args);
+  FFI_RETURN_ERR (sc, lseek (fd, offset, whence) == (off_t) -1
+                  ? gpg_error_from_syserror () : 0);
+}
+
 static pointer
 do_mkdtemp (scheme *sc, pointer args)
 {
@@ -1309,6 +1324,9 @@ ffi_init (scheme *sc, const char *argv0, const char *scriptname,
   ffi_define_constant (sc, STDIN_FILENO);
   ffi_define_constant (sc, STDOUT_FILENO);
   ffi_define_constant (sc, STDERR_FILENO);
+  ffi_define_constant (sc, SEEK_SET);
+  ffi_define_constant (sc, SEEK_CUR);
+  ffi_define_constant (sc, SEEK_END);
 
   ffi_define_function (sc, sleep);
   ffi_define_function (sc, usleep);
@@ -1320,6 +1338,7 @@ ffi_init (scheme *sc, const char *argv0, const char *scriptname,
   ffi_define_function (sc, open);
   ffi_define_function (sc, fdopen);
   ffi_define_function (sc, close);
+  ffi_define_function (sc, seek);
   ffi_define_function_name (sc, "_mkdtemp", mkdtemp);
   ffi_define_function (sc, unlink);
   ffi_define_function (sc, unlink_recursively);
diff --git a/tests/gpgscm/lib.scm b/tests/gpgscm/lib.scm
index 27779e24a..4e19eae60 100644
--- a/tests/gpgscm/lib.scm
+++ b/tests/gpgscm/lib.scm
@@ -204,6 +204,14 @@
 ;; Libc functions.
 ;;
 
+;; Change the read/write offset.
+(ffi-define (seek fd offset whence))
+
+;; Constants for WHENCE.
+(ffi-define SEEK_SET)
+(ffi-define SEEK_CUR)
+(ffi-define SEEK_END)
+
 ;; Get our process id.
 (ffi-define (getpid))