diff --git a/syntax.lisp b/syntax.lisp
index 43d0b7a..534ca35 100644
--- a/syntax.lisp
+++ b/syntax.lisp
@@ -1,5 +1,15 @@
 (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.
+
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (defvar *custom-readtable* (copy-readtable))
+  (setq *readtable* *custom-readtable*))
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
   (defun opening-braket-reader (stream char)
     (declare (ignore char))
@@ -9,7 +19,8 @@
          (,@(read-delimited-list #\] stream t)))))
   (set-macro-character #\[ #'opening-braket-reader)
   ; Using #\) messes up with the editor -,-
-  (set-macro-character #\] (get-macro-character #.(char ")" 0))))
+  (set-macro-character #\] (get-macro-character #.(char ")" 0))
+                       *custom-readtable*))
 
 #+#:excluded (read (make-string-input-stream "[format t \"Hello, ~a!\" _]"))
 
@@ -18,4 +29,5 @@
     (declare (ignore sub-char numarg))
     (loop :while (read-line stream nil nil))
     (values))
-  (set-dispatch-macro-character #\# #\; #'sharp-semicolon-reader))
+  (set-dispatch-macro-character #\# #\; #'sharp-semicolon-reader
+                                *custom-readtable*))
diff --git a/vendor/cl-classified/vendor/ml/mlsyntax.lisp b/vendor/cl-classified/vendor/ml/mlsyntax.lisp
index ab4b622..479e7ac 100644
--- a/vendor/cl-classified/vendor/ml/mlsyntax.lisp
+++ b/vendor/cl-classified/vendor/ml/mlsyntax.lisp
@@ -1,5 +1,15 @@
 (in-package "MLUTILS")
 
+;; 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.
+
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (defvar *custom-readtable* (copy-readtable))
+  (setq *readtable* *custom-readtable*))
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
   (defun opening-braket-reader (stream char)
     (declare (ignore char))
@@ -9,4 +19,15 @@
          (,@(read-delimited-list #\] stream t)))))
   (set-macro-character #\[ #'opening-braket-reader)
   ; Using #\) messes up with the editor -,-
-  (set-macro-character #\] (get-macro-character #.(char ")" 0))))
+  (set-macro-character #\] (get-macro-character #.(char ")" 0))
+                       *custom-readtable*))
+
+#+#:excluded (read (make-string-input-stream "[format t \"Hello, ~a!\" _]"))
+
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (defun sharp-semicolon-reader (stream sub-char numarg)
+    (declare (ignore sub-char numarg))
+    (loop :while (read-line stream nil nil))
+    (values))
+  (set-dispatch-macro-character #\# #\; #'sharp-semicolon-reader
+                                *custom-readtable*))