diff --git a/third_party/gmp/assert.c b/third_party/gmp/assert.c
new file mode 100644
index 0000000..aef95b2
--- /dev/null
+++ b/third_party/gmp/assert.c
@@ -0,0 +1,58 @@
+/* GMP assertion failure handler.
+
+   THE FUNCTIONS IN THIS FILE 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 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 <stdio.h>
+#include <stdlib.h>
+#include "gmp-impl.h"
+
+
+void
+__gmp_assert_header (const char *filename, int linenum)
+{
+  if (filename != NULL && filename[0] != '\0')
+    {
+      fprintf (stderr, "%s:", filename);
+      if (linenum != -1)
+        fprintf (stderr, "%d: ", linenum);
+    }
+}
+
+void
+__gmp_assert_fail (const char *filename, int linenum,
+                   const char *expr)
+{
+  __gmp_assert_header (filename, linenum);
+  fprintf (stderr, "GNU MP assertion failed: %s\n", expr);
+  abort();
+}