diff --git a/src/page-file.rkt b/src/page-file.rkt
index 9be0958..5d4b886 100644
--- a/src/page-file.rkt
+++ b/src/page-file.rkt
@@ -31,7 +31,7 @@
 (define (html-from-url image-url)
   (log-outgoing image-url)
   (define dest-res (easy:head image-url #:timeouts timeouts))
-  (define content-type (easy:response-headers-ref dest-res "Content-Type"))
+  (define content-type (easy:response-headers-ref dest-res 'Content-Type))
   `(cond
     [(eq? content-type #f) ""]
     [(regexp-match? #rx"^image/" content-type)