diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 2d9ae9a99d54..c4169b9bb846 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -273,7 +273,7 @@ in
   fetchhg = callPackage ../build-support/fetchhg { };
 
   # `fetchurl' downloads a file from the network.
-  fetchurl = import ../build-support/fetchurl {
+  fetchurl = makeOverridable (import ../build-support/fetchurl) {
     inherit lib stdenvNoCC;
     curl = buildPackages.curl.override rec {
       # break dependency cycles