diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 34b97fc8c5f4..c720f94257f2 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -232,7 +232,7 @@ rec {
     inherit fetchurl stdenv;
   };
 
-  curl = useFromStdenv (stdenv ? curl) stdenv.curl realCurl;
+  curl = if stdenv ? curl then stdenv.curl else (assert false; null);
 
   realCurl = (import ../tools/networking/curl) {
     inherit fetchurl stdenv zlib;