diff --git a/pkgs/tools/package-management/nix/unstable.nix b/pkgs/tools/package-management/nix/unstable.nix
index d39a13196a8..dd3a6ba3cf0 100644
--- a/pkgs/tools/package-management/nix/unstable.nix
+++ b/pkgs/tools/package-management/nix/unstable.nix
@@ -5,11 +5,11 @@
 }:
 
 stdenv.mkDerivation rec {
-  name = "nix-1.9pre4083_5114a07";
+  name = "nix-1.9pre4087_afa433e";
 
   src = fetchurl {
-    url = "http://hydra.nixos.org/build/20650421/download/4/${name}.tar.xz";
-    sha256 = "971fdd36bcf39c7e6ce9ef12dbfe09c98d2be3275e482ca2dbacb2e668f0dff9";
+    url = "http://hydra.nixos.org/build/21053128/download/4/${name}.tar.xz";
+    sha256 = "05dda3644ed68364bbff87d0ec662ca18d8542f921683cb2e1f308281d6bf384";
   };
 
   nativeBuildInputs = [ perl pkgconfig ];