diff --git a/Makefile b/Makefile
deleted file mode 100644
index 9cdf6b6..0000000
--- a/Makefile
+++ /dev/null
@@ -1,14 +0,0 @@
-LISP ?= sbcl
-
-default: build
-
-# https://lispcookbook.github.io/cl-cookbook/scripting.html
-build:
-	$(LISP) --eval '(require :asdf)' \
-		--eval '(load "ywatds.asd")' \
-		--eval '(asdf:load-system "ywatds")' \
-		--eval '(asdf:make :ywatds)' \
-		--eval '(quit)'
-
-clean:
-	-rm ywatds *~ *.backup API.md
diff --git a/build.lisp b/build.lisp
new file mode 100644
index 0000000..0abdd9e
--- /dev/null
+++ b/build.lisp
@@ -0,0 +1,5 @@
+(require :asdf)
+(load "ywatds.asd")
+(asdf:load-system :ywatds)
+(asdf:make :ywatds)
+(quit)
diff --git a/tracks/conns.lisp b/tracks/conns.lisp
index 5039dca..ba6a613 100644
--- a/tracks/conns.lisp
+++ b/tracks/conns.lisp
@@ -4,8 +4,8 @@
 (defparameter *conns-shared* nil)
 
 (defstruct trackside
-  (:pos (error "no coordinates specified") :type aux:v3d)
-  (:side (error "no side specified") :type (integer 0 15)))
+  (:pos (error "no coordinates specified") :type aux:v3d :read-only t)
+  (:side (error "no side specified") :type (integer 0 15) :read-only t))
 
 (defmacro trackside (pos side)
   (alexandria:once-only
@@ -22,8 +22,8 @@
     (json:encode-json (list (cons "p" p) (cons "s" side)))))
 
 (defstruct dir
-  (:c 0 :type (integer 0 15))
-  (:r 0 :type (integer 0 1)))
+  (:c 0 :type (integer 0 15) :read-only t)
+  (:r 0 :type (integer 0 1) :read-only t))
 
 (defmethod print-object ((obj dir) s)
   (print-unreadable-object (obj s)