diff --git a/gnu/packages/guile.scm b/gnu/packages/guile.scm
index 96d5288e4a284de63b4857b8b2d4b79ce2af35f9..a4203f0f3b936d96803bcb9562e44e0a6c20b32d 100644
--- a/gnu/packages/guile.scm
+++ b/gnu/packages/guile.scm
@@ -812,7 +812,7 @@ (define-public guile-sly
     (version "0.1")
     (source (origin
               (method url-fetch)
-              (uri (string-append "http://files.dthompson.us/sly/sly-"
+              (uri (string-append "https://files.dthompson.us/sly/sly-"
                                   version ".tar.gz"))
               (sha256
                (base32