diff --git a/nix/sources.json b/nix/sources.json
index ec6efa9..63a748c 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -55,6 +55,18 @@
         "url_template": "https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/archive/<version>/nixos-mailserver-<version>.tar.gz",
         "version": "5675b122a947b40e551438df6a623efad19fd2e7"
     },
+    "nixos-stable": {
+        "branch": "nixos-21.05",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "530a53dcbc9437363471167a5e4762c5fcfa34a1",
+        "sha256": "11d9m0c4r4kpr3jx3cqblw6ld4d8dwcfv1lk68ipp4c87knwv7fb",
+        "type": "tarball",
+        "url": "https://github.com/nixos/nixpkgs/archive/530a53dcbc9437363471167a5e4762c5fcfa34a1.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "nixpkgs": {
         "branch": "nixos-unstable",
         "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
diff --git a/nixos/physical/fractal.nix b/nixos/physical/fractal.nix
index 8fa54de..795af36 100644
--- a/nixos/physical/fractal.nix
+++ b/nixos/physical/fractal.nix
@@ -31,6 +31,6 @@ in {
     fsType = "zfs";
   };
 
-  nix.maxJobs = 4;
+  nix.settings.max-jobs = 4;
   services.avahi.interfaces = [ "enp2s0" ];
 }
diff --git a/nixos/physical/xps9360-hardware-config.nix b/nixos/physical/xps9360-hardware-config.nix
index 4889d73..655b66a 100644
--- a/nixos/physical/xps9360-hardware-config.nix
+++ b/nixos/physical/xps9360-hardware-config.nix
@@ -25,7 +25,7 @@
   swapDevices =
     [{ device = "/dev/disk/by-uuid/198ddaba-a849-41de-993d-862c2d37937a"; }];
 
-  nix.maxJobs = lib.mkDefault 4;
+  nix.settings.max-jobs = lib.mkDefault 4;
   powerManagement.cpuFreqGovernor = lib.mkDefault "powersave";
   # high-resolution display
   hardware.video.hidpi.enable = lib.mkDefault true;
diff --git a/pkgs/default.nix b/pkgs/default.nix
index 367070a..b62689b 100644
--- a/pkgs/default.nix
+++ b/pkgs/default.nix
@@ -3,7 +3,7 @@
   yori-cc = super.callPackage ./yori-cc.nix { };
 
   ftb = super.callPackage ./ftb.nix {};
-  pyroscope = super.callPackage ./pyroscope {};
+  pyroscope = (import (import ../nix/sources.nix).nixos-stable {}).callPackage ./pyroscope {}; # TODO: update this
   #lejos = super.callPackage ../pkgs/lejos.nix {};
 
   weiightminder = super.callPackage (builtins.fetchGit {