diff --git a/project-requires.rkt b/project-requires.rkt
index 443e7e1..ab68113 100644
--- a/project-requires.rkt
+++ b/project-requires.rkt
@@ -4,7 +4,8 @@
 
 (define (project-require-file? path)
   (define path-string (path->string path))
-  (equal? (substring path-string (- (string-length path-string) 3) (string-length path-string)) "rkt"))
+  (define racket-ext "rkt")
+  (equal? (substring path-string (- (string-length path-string) (string-length racket-ext)) (string-length path-string)) racket-ext))
 
 ;; list of all eligible requires in project require directory
 (define (get-project-require-files)
@@ -12,7 +13,7 @@
   (and (directory-exists? extras-directory)
        ;; #:build? option returns complete paths (instead of just file names)
        (let ([files (filter project-require-file? (directory-list extras-directory #:build? #t))])
-         (and (not (equal? '() files)) files))))
+         (and (not (equal? null files)) files))))
 
 (module+ main
 (parameterize ([world:current-project-root (string->path "/Users/mb/git/bpt/")])