diff --git a/lib/riscv64-mes-mescc/setjmp.c b/lib/riscv64-mes-mescc/setjmp.c
new file mode 100644
index 00000000..4e3a4f9d
--- /dev/null
+++ b/lib/riscv64-mes-mescc/setjmp.c
@@ -0,0 +1,47 @@
+/* -*-comment-start: "//";comment-end:""-*-
+ * GNU Mes --- Maxwell Equations of Software
+ * Copyright © 2017,2018,2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+ * Copyright © 2021 W. J. van der Laan <laanwj@protonmail.com>
+ *
+ * This file is part of GNU Mes.
+ *
+ * GNU Mes is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * GNU Mes is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <setjmp.h>
+#include <stdlib.h>
+
+void
+longjmp (jmp_buf env, int val)
+{
+  val = val == 0 ? 1 : val;
+  asm ("ld_____%fp,0x10(%fp)"); // env*
+
+  asm ("ld_____%t0,0x8(%fp)");  // env.__pc
+  asm ("ld_____%sp,0x10(%fp)"); // env.__sp
+  asm ("ld_____%fp,0x0(%fp)");  // env.__bp
+  asm ("jr_____%t0");
+  // not reached
+  exit (42);
+}
+
+int
+setjmp (__jmp_buf * env)
+{
+  long *p = (long *) &env;
+  env[0].__bp = p[-2];
+  env[0].__pc = p[-1];
+  env[0].__sp = (long) &env;
+  return 0;
+}