diff --git a/syntax.lisp b/syntax.lisp
index 43d0b7a..26bcb18 100644
--- a/syntax.lisp
+++ b/syntax.lisp
@@ -1,5 +1,12 @@
 (in-package :aoc)
 
+;; If we don't copy the system readtable first, Allregro will fail with
+;; the following error:
+;;
+;;     Attempt to set macro in system readtable #<readtable @ #x20115b5a>;
+;;     copy readtable first.
+(setq *readtable* (copy-readtable)) 
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
   (defun opening-braket-reader (stream char)
     (declare (ignore char))