diff --git a/third_party/gmp/errno.c b/third_party/gmp/errno.c
new file mode 100644
index 0000000..b4be555
--- /dev/null
+++ b/third_party/gmp/errno.c
@@ -0,0 +1,72 @@
+/* gmp_errno, __gmp_exception -- exception handling and reporting.
+
+   THE FUNCTIONS IN THIS FILE, APART FROM gmp_errno, ARE FOR INTERNAL USE
+   ONLY.  THEY'RE ALMOST CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR
+   DISAPPEAR COMPLETELY IN FUTURE GNU MP RELEASES.
+
+Copyright 2000, 2001, 2003 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of either:
+
+  * the GNU Lesser General Public License as published by the Free
+    Software Foundation; either version 3 of the License, or (at your
+    option) any later version.
+
+or
+
+  * the GNU General Public License as published by the Free Software
+    Foundation; either version 2 of the License, or (at your option) any
+    later version.
+
+or both in parallel, as here.
+
+The GNU MP Library 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 copies of the GNU General Public License and the
+GNU Lesser General Public License along with the GNU MP Library.  If not,
+see https://www.gnu.org/licenses/.  */
+
+#include <stdlib.h>
+
+#include <signal.h>
+
+#include "gmp-impl.h"
+
+int gmp_errno = 0;
+
+
+/* Use SIGFPE on systems which have it. Otherwise, deliberate divide
+   by zero, which triggers an exception on most systems. On those
+   where it doesn't, for example power and powerpc, use abort instead. */
+void
+__gmp_exception (int error_bit)
+{
+  gmp_errno |= error_bit;
+#ifdef SIGFPE
+  raise (SIGFPE);
+#else
+  __gmp_junk = 10 / __gmp_0;
+#endif
+  abort ();
+}
+
+
+/* These functions minimize the amount of code required in functions raising
+   exceptions.  Since they're "noreturn" and don't take any parameters, a
+   test and call might even come out as a simple conditional jump.  */
+void
+__gmp_sqrt_of_negative (void)
+{
+  __gmp_exception (GMP_ERROR_SQRT_OF_NEGATIVE);
+}
+void
+__gmp_divide_by_zero (void)
+{
+  __gmp_exception (GMP_ERROR_DIVISION_BY_ZERO);
+}