diff --git a/pollen-file-tools.rkt b/pollen-file-tools.rkt
index 88f0e8d..f5f401c 100644
--- a/pollen-file-tools.rkt
+++ b/pollen-file-tools.rkt
@@ -130,7 +130,8 @@
   (any/c . -> . boolean?)
   (->boolean (or path? string? symbol?)))
 
-
+;; todo: tighten these input contracts
+;; so that, say, a source-path cannot be input for make-preproc-source-path
 (define/contract (make-preproc-source-path path)
   (path? . -> . path?)
   (add-ext path POLLEN_PREPROC_EXT))