diff --git a/Makefile b/Makefile
index 3144d1129..077adc0f1 100644
--- a/Makefile
+++ b/Makefile
@@ -12,8 +12,8 @@ ifneq ($(J),)
 	jobs_args := -j$(J)
 endif
 
-ifneq ($(CORES),)
-	cores_args := --cores $(CORES)
+ifneq ($(C),)
+	cores_args := --cores $(C)
 endif
 
 nix_args := $(keep_going_args) $(jobs_args) $(cores_args)
diff --git a/hacking/nix/default.nix b/hacking/nix/default.nix
index deef4515a..9b2353b36 100644
--- a/hacking/nix/default.nix
+++ b/hacking/nix/default.nix
@@ -8,11 +8,11 @@ let
 
   defaultNixpkgsPath =
     let
-      rev = "1811c4fec88995679397d6fa20f4f3395a0bebe5";
+      rev = "3add434811677ed7fcd013c136806f8c6f410545";
     in
       builtins.fetchTarball {
         url = "https://github.com/coliasgroup/nixpkgs/archive/refs/tags/keep/${builtins.substring 0 32 rev}.tar.gz";
-        sha256 = "sha256:0ad2c7vlr9fidzjjg8szigfhmp1gvlf62ckd6cir8ymrxc93pby7";
+        sha256 = "sha256:1pi5chvv5jld5jb8x0j4ni4w60m4x5dajfwhk1nh2j1kjxxrk1mk";
       };
 
 in
diff --git a/hacking/nix/scope/capdl-tool/Makefile b/hacking/nix/scope/capdl-tool/Makefile
index fde3c97b7..1f19860ee 100644
--- a/hacking/nix/scope/capdl-tool/Makefile
+++ b/hacking/nix/scope/capdl-tool/Makefile
@@ -8,7 +8,7 @@ top_level := ../../../..
 capdl := $(top_level)/../x/capdl/capDL-tool
 cabal2nix := $(shell nix-build $(top_level) -A pkgs.build.cabal2nix --no-out-link)/bin/cabal2nix
 
-all := capDL-tool.nix base-compat-0-12-2.nix base-compat-batteries-0-12-2.nix
+all := capDL-tool.nix base-compat-0-12-2.nix base-compat-batteries-0-12-2.nix MissingH-1.5.0.1.nix
 
 .PHONY: all $(all)
 all: $(all)
@@ -21,3 +21,6 @@ base-compat-0-12-2.nix:
 
 base-compat-batteries-0-12-2.nix:
 	$(cabal2nix) cabal://base-compat-batteries-0.12.2 > $@
+
+MissingH-1.5.0.1.nix:
+	$(cabal2nix) cabal://MissingH-1.5.0.1 > $@
diff --git a/hacking/nix/scope/capdl-tool/MissingH-1.5.0.1.nix b/hacking/nix/scope/capdl-tool/MissingH-1.5.0.1.nix
new file mode 100644
index 000000000..c3203f279
--- /dev/null
+++ b/hacking/nix/scope/capdl-tool/MissingH-1.5.0.1.nix
@@ -0,0 +1,22 @@
+{ mkDerivation, array, base, containers, directory, filepath
+, hslogger, HUnit, lib, mtl, network, network-bsd, old-locale
+, old-time, parsec, process, regex-compat, time, unix
+}:
+mkDerivation {
+  pname = "MissingH";
+  version = "1.5.0.1";
+  sha256 = "cb2fa4a62a609ec6bcfa2eab6ae6d34c6f5bfba523fed8dc0c055b3176732231";
+  revision = "2";
+  editedCabalFile = "11d922r06p00gcgzhb29hhjkq8ajy1xbqdiwdpbmhp2ar7fw7g9l";
+  libraryHaskellDepends = [
+    array base containers directory filepath hslogger mtl network
+    network-bsd old-locale old-time parsec process regex-compat time
+    unix
+  ];
+  testHaskellDepends = [
+    base containers directory filepath HUnit old-time parsec
+    regex-compat time unix
+  ];
+  description = "Large utility library";
+  license = lib.licenses.bsd3;
+}
diff --git a/hacking/nix/scope/capdl-tool/default.nix b/hacking/nix/scope/capdl-tool/default.nix
index 095819821..19027d390 100644
--- a/hacking/nix/scope/capdl-tool/default.nix
+++ b/hacking/nix/scope/capdl-tool/default.nix
@@ -14,6 +14,7 @@ let
     overrides = self: super: {
       base-compat = self.callPackage ./base-compat-0-12-2.nix {};
       base-compat-batteries = self.callPackage ./base-compat-batteries-0-12-2.nix {};
+      MissingH = self.callPackage ./MissingH-1.5.0.1.nix {};
       capDL-tool = self.callPackage ./capDL-tool.nix {
         inherit sources;
       };
diff --git a/hacking/nix/scope/default.nix b/hacking/nix/scope/default.nix
index c6974a336..6e97c4c4c 100644
--- a/hacking/nix/scope/default.nix
+++ b/hacking/nix/scope/default.nix
@@ -238,7 +238,7 @@ superCallPackage ../rust-utils {} self //
 
   overrideWorldScope = self: super: {};
 
-  mkWorldFrom = newScope: unelaboratedWorldConfig: (lib.makeScope newScope (callPackage ./world {} unelaboratedWorldConfig)).overrideScope' overrideWorldScope;
+  mkWorldFrom = newScope: unelaboratedWorldConfig: (lib.makeScope newScope (callPackage ./world {} unelaboratedWorldConfig)).overrideScope overrideWorldScope;
 
   mkWorld = mkWorldFrom newScope;
 
diff --git a/hacking/nix/scope/sel4test/default.nix b/hacking/nix/scope/sel4test/default.nix
index c762d7656..dd9e661bf 100644
--- a/hacking/nix/scope/sel4test/default.nix
+++ b/hacking/nix/scope/sel4test/default.nix
@@ -55,7 +55,7 @@ let
   tests = stdenv.mkDerivation {
     name = "sel4test";
 
-    src = fetchRepoProject {
+    src = buildPackages.fetchRepoProject {
       name = "sel4test";
       manifest = "https://github.com/seL4/sel4test-manifest.git";
       rev = "8bf6fd506a0546866ba5fbd7396f497d5a056f5c";
diff --git a/hacking/nix/scope/shell-for-hacking.nix b/hacking/nix/scope/shell-for-hacking.nix
index 5965dd223..7f6a892bf 100644
--- a/hacking/nix/scope/shell-for-hacking.nix
+++ b/hacking/nix/scope/shell-for-hacking.nix
@@ -7,7 +7,7 @@
 { lib, stdenv, hostPlatform, buildPackages
 , mkShell
 
-, pkgconfig
+, pkg-config
 , git
 , cacert
 , rustup, rustPlatform
@@ -34,7 +34,7 @@ mkShell (shellForMakefile.apply {
   ];
 
   nativeBuildInputs = [
-    pkgconfig
+    pkg-config
     git
     cacert
     rustup