diff --git a/pkgs/os-specific/linux/aufs/3.nix b/pkgs/os-specific/linux/aufs/3.nix
index 130fd5075cd5..255804a31de9 100644
--- a/pkgs/os-specific/linux/aufs/3.nix
+++ b/pkgs/os-specific/linux/aufs/3.nix
@@ -33,6 +33,7 @@ stdenv.mkDerivation {
     '';
 
   passthru = { inherit patch; };
+
   meta = {
     description = "Another Unionfs implementation for Linux (third generation)";
     homepage = http://aufs.sourceforge.net/;
diff --git a/pkgs/stdenv/generic/default.nix b/pkgs/stdenv/generic/default.nix
index 852be9612fb5..b6836ca8d79c 100644
--- a/pkgs/stdenv/generic/default.nix
+++ b/pkgs/stdenv/generic/default.nix
@@ -10,7 +10,7 @@ let
 
   lib = import ../../lib;
 
-  disallowUnfree = builtins.getEnv "HYDRA_DISALLOW_UNFREE" == "1";
+  allowUnfree = config.allowUnfree or true && builtins.getEnv "HYDRA_DISALLOW_UNFREE" != "1";
 
   stdenvGenerator = setupScript: rec {
 
@@ -41,7 +41,7 @@ let
         # Add a utility function to produce derivations that use this
         # stdenv and its shell.
         mkDerivation = attrs:
-          if disallowUnfree && attrs.meta.license or "" == "unfree" then
+          if !allowUnfree && attrs.meta.license or "" == "unfree" then
             throw "package ‘${attrs.name}’ has an unfree license, refusing to evaluate"
           else
           (derivation (
diff --git a/pkgs/top-level/release-lib.nix b/pkgs/top-level/release-lib.nix
index 4a5f7602d02d..d03f2724e1f0 100644
--- a/pkgs/top-level/release-lib.nix
+++ b/pkgs/top-level/release-lib.nix
@@ -1,7 +1,11 @@
 rec {
-  allPackages = import ./all-packages.nix;
 
-  pkgs = allPackages {};
+  # Ensure that we don't build packages marked as unfree.
+  allPackages = args: import ./all-packages.nix (args // {
+    config.allowUnfree = false;
+  });
+
+  pkgs = allPackages { };
 
   /* !!! Hack: poor man's memoisation function.  Necessary for prevent
      Nixpkgs from being evaluated again and again for every