diff --git a/lib/stdlib/qsort.c b/lib/stdlib/qsort.c
index 4f3e61cb..24ab9a48 100644
--- a/lib/stdlib/qsort.c
+++ b/lib/stdlib/qsort.c
@@ -1,6 +1,6 @@
 /* -*-comment-start: "//";comment-end:""-*-
  * GNU Mes --- Maxwell Equations of Software
- * Copyright © 2017,2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+ * Copyright © 2017,2018,2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
  *
  * This file is part of GNU Mes.
  *
@@ -18,13 +18,15 @@
  * along with GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 
 void
 qswap (void *a, void *b, size_t size)
 {
-  char *buf[8];
+  char buf[128];
+  assert (size <= sizeof (buf));
   memcpy (buf, a, size);
   memcpy (a, b, size);
   memcpy (b, buf, size);