thodg/cl-unix-cybernetics

diff --git a/Makefile b/Makefile
index ae28afd..06777b7 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ RELEASE_TARBALL = ${PACKAGE}-${VERSION}.tar.gz
 RELEASE_DEPS_TARBALL = ${PACKAGE}-${VERSION}.deps.tar.gz
 PROGRAM = build/cl-unix-cybernetics
 PREFIX = /usr/local
-LISP = sbcl --dynamic-space-size 2048
+LISP = sbcl --dynamic-space-size 1024
 LISP_LOAD = ${LISP} --load
 CLEANFILES = build/*
 DISTCLEANFILES = ${RELEASE_DIR} ${RELEASE_TARBALL} ${RELEASE_DEPS_TARBALL}
diff --git a/prepare-build.lisp b/prepare-build.lisp
index 9b63b72..c616903 100644
--- a/prepare-build.lisp
+++ b/prepare-build.lisp
@@ -148,9 +148,10 @@
   (let* ((asd (asdf:system-source-file system))
          (name (substitute #\- #\/ (asdf:component-name system)))
          (sbf (concatenate 'string "build/" name ".lisp")))
-    (when (or (not (probe-file sbf))
-              (< (file-write-date sbf)
-                 (file-write-date asd)))
+    (when (and asd
+               (or (not (probe-file sbf))
+                   (< (file-write-date sbf)
+                      (file-write-date asd))))
       (write-system-build-file system sbf))
     sbf))