--- a/contrib/make-contrib.lisp
+++ b/contrib/make-contrib.lisp
@@ -115,12 +115,21 @@
                              :direction :output :if-exists :supersede
                              :if-does-not-exist :create)
           (format asd "(defsystem :~A :class require-system)~%" *system*))
-        (sb-sys:os-exit
-         (process-status
-          (run-program #+unix "/bin/cat" #-unix "cat" outputs
-                       ;; probably is /usr/bin/cat.exe but let's not assume that
-                       #-unix :search #-unix t
-                       :output joined :if-output-exists :supersede)))))))
+        (cat outputs joined)))))
+
+(defun cat (inputs output)
+  (with-open-file (out output :element-type '(unsigned-byte 8)
+                              :direction :output
+                              :if-exists :supersede
+                              :if-does-not-exist :create)
+    (dolist (pathname inputs)
+      (with-open-file (in pathname :element-type '(unsigned-byte 8))
+        (let ((buffer (make-array 4096 :element-type '(unsigned-byte 8))))
+          (declare (dynamic-extent buffer))
+          (loop with length = (file-length in)
+                for position = (read-sequence buffer in)
+                while (plusp position)
+                do (write-sequence buffer out :end position)))))))
 
 (compile 'perform)
 (let ((form (with-open-file (f (format nil "~A.asd" *system*))