diff --git a/pkgs/development/ocaml-modules/base64/default.nix b/pkgs/development/ocaml-modules/base64/default.nix
index 08b028c874ee..0638e50566e5 100644
--- a/pkgs/development/ocaml-modules/base64/default.nix
+++ b/pkgs/development/ocaml-modules/base64/default.nix
@@ -9,14 +9,14 @@
   rresult,
 }:
 
-buildDunePackage rec {
+buildDunePackage (finalAttrs: {
   pname = "base64";
   version = "3.5.2";
 
   minimalOCamlVersion = "4.07";
 
   src = fetchurl {
-    url = "https://github.com/mirage/ocaml-base64/releases/download/v${version}/base64-${version}.tbz";
+    url = "https://github.com/mirage/ocaml-base64/releases/download/v${finalAttrs.version}/base64-${finalAttrs.version}.tbz";
     hash = "sha256-s/XOMBqnLHAy75C+IzLXL/OWKSLADuKuxryt4Yei9Zs=";
   };
 
@@ -36,4 +36,4 @@ buildDunePackage rec {
     license = lib.licenses.isc;
     maintainers = with lib.maintainers; [ vbgl ];
   };
-}
+})