diff --git a/pkgs/tools/package-management/nix/unstable.nix b/pkgs/tools/package-management/nix/unstable.nix
index 1ed19bb9b25..c3743c7583d 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-1.1pre2749_ccc52ad";
+  name = "nix-1.1pre2789_7671018";
 
   src = fetchurl {
-    url = "http://hydra.nixos.org/build/2841643/download/4/${name}.tar.bz2";
-    sha256 = "eae2135dd70d2734080ee644a597e131f60e71991dbabdabf67ab0818ff1f6fc";
+    url = "http://hydra.nixos.org/build/2949617/download/4/${name}.tar.bz2";
+    sha256 = "64ae790a7326893dc92f77c297862c4a74b1381c17b5fc559428fb7988421109";
   };
 
   buildNativeInputs = [ perl pkgconfig ];
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 55e16d3d879..1e4219e1db9 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -8642,14 +8642,10 @@ let
     stateDir = getConfig [ "nix" "stateDir" ] "/nix/var";
   };
 
-  nixUnstable = nix;
-
-  /*
   nixUnstable = callPackage ../tools/package-management/nix/unstable.nix {
     storeDir = getConfig [ "nix" "storeDir" ] "/nix/store";
     stateDir = getConfig [ "nix" "stateDir" ] "/nix/var";
   };
-  */
 
   nixCustomFun = src: preConfigure: enableScripts: configureFlags:
     import ../tools/package-management/nix/custom.nix {