diff --git a/default.nix b/default.nix
index 1317ed5..1c7323f 100644
--- a/default.nix
+++ b/default.nix
@@ -1,23 +1,30 @@
-{ nixpkgs ? import <nixpkgs> }:
-
-with builtins;
-
 let
-  nixpkgs' = nixpkgs {
-    config.allowUnsupportedSystem = true;
-    crossSystem = {
-      isx86_64 = true;
-      isGenode = true;
-      imports = [ ./platform.nix ];
+  pkgOverlay = self: super:
+    # Overlay of locally defined packages
+    {
+      genode = super.callPackage ./upstream { };
+      dhall = super.callPackage ./dhall { };
     };
-    overlays = [ (import ./overlay) ];
+
+  toolchainOverlay = import ./toolchain-overlay;
+  # Overlay of toolchain patches
+
+  nixpkgs' = builtins.fetchGit {
+    # A branch of Nixpkgs with a custom "crossSystem" mechanism
+    url = "https://github.com/ehmry/nixpkgs.git";
+    ref = "hybrid";
+    rev = "e4d734ace275cae70a776771d034c051956c9cab";
   };
 
-in rec {
-  nixpkgs = nixpkgs';
-
-  dhall = import ./dhall { inherit nixpkgs; };
-
-  upstream = import ./upstream { inherit nixpkgs; };
+in { nixpkgs ? import nixpkgs' }:
 
+nixpkgs {
+  # Evaluate an overlayed Nixpkgs for a Genode target
+  config.allowUnsupportedSystem = true;
+  crossSystem = {
+    isx86_64 = true;
+    isGenode = true;
+    imports = [ ./platform.nix ];
+  };
+  overlays = [ toolchainOverlay pkgOverlay ];
 }
diff --git a/dhall/default.nix b/dhall/default.nix
index ffe8d43..29bda3e 100644
--- a/dhall/default.nix
+++ b/dhall/default.nix
@@ -1,8 +1,7 @@
-{ nixpkgs }:
+{ callPackage }:
 
 rec {
-
   prelude = prelude_9_0_0;
-  prelude_9_0_0 = nixpkgs.callPackage ./prelude-9.0.0.nix {};
-  genode = nixpkgs.callPackage ./genode.nix {};
+  prelude_9_0_0 = callPackage ./prelude-9.0.0.nix { };
+  genode = callPackage ./genode.nix { };
 }
diff --git a/overlay/Genode.cmake b/toolchain-overlay/Genode.cmake
similarity index 100%
rename from overlay/Genode.cmake
rename to toolchain-overlay/Genode.cmake
diff --git a/overlay/binutils.patch b/toolchain-overlay/binutils.patch
similarity index 100%
rename from overlay/binutils.patch
rename to toolchain-overlay/binutils.patch
diff --git a/overlay/clang.patch b/toolchain-overlay/clang.patch
similarity index 100%
rename from overlay/clang.patch
rename to toolchain-overlay/clang.patch
diff --git a/overlay/compiler-rt.patch b/toolchain-overlay/compiler-rt.patch
similarity index 100%
rename from overlay/compiler-rt.patch
rename to toolchain-overlay/compiler-rt.patch
diff --git a/overlay/default.nix b/toolchain-overlay/default.nix
similarity index 100%
rename from overlay/default.nix
rename to toolchain-overlay/default.nix
diff --git a/overlay/headers/default.nix b/toolchain-overlay/headers/default.nix
similarity index 100%
rename from overlay/headers/default.nix
rename to toolchain-overlay/headers/default.nix
diff --git a/overlay/libc++.patch b/toolchain-overlay/libc++.patch
similarity index 100%
rename from overlay/libc++.patch
rename to toolchain-overlay/libc++.patch
diff --git a/overlay/libc/MB_CUR_MAX.patch b/toolchain-overlay/libc/MB_CUR_MAX.patch
similarity index 100%
rename from overlay/libc/MB_CUR_MAX.patch
rename to toolchain-overlay/libc/MB_CUR_MAX.patch
diff --git a/overlay/libc/_CurrentRuneLocale.patch b/toolchain-overlay/libc/_CurrentRuneLocale.patch
similarity index 100%
rename from overlay/libc/_CurrentRuneLocale.patch
rename to toolchain-overlay/libc/_CurrentRuneLocale.patch
diff --git a/overlay/libc/cdefs_no_hidden.patch b/toolchain-overlay/libc/cdefs_no_hidden.patch
similarity index 100%
rename from overlay/libc/cdefs_no_hidden.patch
rename to toolchain-overlay/libc/cdefs_no_hidden.patch
diff --git a/overlay/libc/default.nix b/toolchain-overlay/libc/default.nix
similarity index 100%
rename from overlay/libc/default.nix
rename to toolchain-overlay/libc/default.nix
diff --git a/overlay/libc/gdtoa.patch b/toolchain-overlay/libc/gdtoa.patch
similarity index 100%
rename from overlay/libc/gdtoa.patch
rename to toolchain-overlay/libc/gdtoa.patch
diff --git a/overlay/libc/genode_rel.ld b/toolchain-overlay/libc/genode_rel.ld
similarity index 100%
rename from overlay/libc/genode_rel.ld
rename to toolchain-overlay/libc/genode_rel.ld
diff --git a/overlay/libc/libc-builder.sh b/toolchain-overlay/libc/libc-builder.sh
similarity index 100%
rename from overlay/libc/libc-builder.sh
rename to toolchain-overlay/libc/libc-builder.sh
diff --git a/overlay/libc/libc.pc.in b/toolchain-overlay/libc/libc.pc.in
similarity index 100%
rename from overlay/libc/libc.pc.in
rename to toolchain-overlay/libc/libc.pc.in
diff --git a/overlay/libc/libc.symbols b/toolchain-overlay/libc/libc.symbols
similarity index 100%
rename from overlay/libc/libc.symbols
rename to toolchain-overlay/libc/libc.symbols
diff --git a/overlay/libc/log2.patch b/toolchain-overlay/libc/log2.patch
similarity index 100%
rename from overlay/libc/log2.patch
rename to toolchain-overlay/libc/log2.patch
diff --git a/overlay/libc/mktime.patch b/toolchain-overlay/libc/mktime.patch
similarity index 100%
rename from overlay/libc/mktime.patch
rename to toolchain-overlay/libc/mktime.patch
diff --git a/overlay/libc/printfcommon.patch b/toolchain-overlay/libc/printfcommon.patch
similarity index 100%
rename from overlay/libc/printfcommon.patch
rename to toolchain-overlay/libc/printfcommon.patch
diff --git a/overlay/libc/rcmd.patch b/toolchain-overlay/libc/rcmd.patch
similarity index 100%
rename from overlay/libc/rcmd.patch
rename to toolchain-overlay/libc/rcmd.patch
diff --git a/overlay/libc/res_init_c.patch b/toolchain-overlay/libc/res_init_c.patch
similarity index 100%
rename from overlay/libc/res_init_c.patch
rename to toolchain-overlay/libc/res_init_c.patch
diff --git a/overlay/libc/runetype.patch b/toolchain-overlay/libc/runetype.patch
similarity index 100%
rename from overlay/libc/runetype.patch
rename to toolchain-overlay/libc/runetype.patch
diff --git a/overlay/libc/semaphore.patch b/toolchain-overlay/libc/semaphore.patch
similarity index 100%
rename from overlay/libc/semaphore.patch
rename to toolchain-overlay/libc/semaphore.patch
diff --git a/overlay/libc/thread_local.patch b/toolchain-overlay/libc/thread_local.patch
similarity index 100%
rename from overlay/libc/thread_local.patch
rename to toolchain-overlay/libc/thread_local.patch
diff --git a/overlay/libc/types.patch b/toolchain-overlay/libc/types.patch
similarity index 100%
rename from overlay/libc/types.patch
rename to toolchain-overlay/libc/types.patch
diff --git a/overlay/libc/vfwprintf_c_warn.patch b/toolchain-overlay/libc/vfwprintf_c_warn.patch
similarity index 100%
rename from overlay/libc/vfwprintf_c_warn.patch
rename to toolchain-overlay/libc/vfwprintf_c_warn.patch
diff --git a/overlay/libc/xlocale.patch b/toolchain-overlay/libc/xlocale.patch
similarity index 100%
rename from overlay/libc/xlocale.patch
rename to toolchain-overlay/libc/xlocale.patch
diff --git a/overlay/libc/xlocale_private.patch b/toolchain-overlay/libc/xlocale_private.patch
similarity index 100%
rename from overlay/libc/xlocale_private.patch
rename to toolchain-overlay/libc/xlocale_private.patch
diff --git a/overlay/libc/xprintf_float.patch b/toolchain-overlay/libc/xprintf_float.patch
similarity index 100%
rename from overlay/libc/xprintf_float.patch
rename to toolchain-overlay/libc/xprintf_float.patch
diff --git a/overlay/llvm.patch b/toolchain-overlay/llvm.patch
similarity index 100%
rename from overlay/llvm.patch
rename to toolchain-overlay/llvm.patch
diff --git a/upstream/default.nix b/upstream/default.nix
index 60037d4..e78d5f1 100644
--- a/upstream/default.nix
+++ b/upstream/default.nix
@@ -1,30 +1,34 @@
-{ nixpkgs }:
+{ stdenv, buildPackages, fetchgit, llvmPackages }:
 
 let
-  inherit (nixpkgs.stdenv) lib targetPlatform;
-  specs = with targetPlatform;
-    [ ] ++ lib.optional is32bit "32bit" ++ lib.optional is64bit "64bit"
-    ++ lib.optional isAarch32 "arm" ++ lib.optional isAarch64 "arm_64"
-    ++ lib.optional isRiscV "riscv" ++ lib.optional isx86 "x86"
-    ++ lib.optional isx86_32 "x86_32" ++ lib.optional isx86_64 "x86_64";
+  inherit (stdenv) lib targetPlatform;
+  specs = with targetPlatform; []
+    ++ lib.optional is32bit "32bit"
+    ++ lib.optional is64bit "64bit"
+    ++ lib.optional isAarch32 "arm"
+    ++ lib.optional isAarch64 "arm_64"
+    ++ lib.optional isRiscV "riscv"
+    ++ lib.optional isx86 "x86"
+    ++ lib.optional isx86_32 "x86_32"
+    ++ lib.optional isx86_64 "x86_64";
 
   version = "19.07";
-  buildRepo = repo: nativeBuildInputs:
+  buildRepo = repo:
 
-    nixpkgs.stdenv.mkDerivation {
+    stdenv.mkDerivation {
       name = "genode-${repo}-${version}";
       outputs = [ "out" "dev" ];
-      inherit repo nativeBuildInputs specs version;
+      inherit repo specs version;
 
-      LIBCXX = nixpkgs.llvmPackages.libcxx;
-      LIBCXXABI = nixpkgs.llvmPackages.libcxxabi;
-      LIBUNWIND = nixpkgs.llvmPackages.libunwind;
-      HOST_LIBC = nixpkgs.buildPackages.glibc.dev;
+      HOST_LIBC = buildPackages.glibc.dev;
+      LIBCXX = llvmPackages.libcxx;
+      LIBCXXABI = llvmPackages.libcxxabi;
+      LIBUNWIND = llvmPackages.libunwind;
 
       LIBUNWIND_BAREMETAL =
-        nixpkgs.llvmPackages.libunwind.override { isBaremetal = true; };
+        llvmPackages.libunwind.override { isBaremetal = true; };
 
-      src = nixpkgs.fetchgit {
+      src = fetchgit {
         url = "https://git.sr.ht/~ehmry/genode";
         rev = "d28abff776f94dc876662eb7dcdf5a6e81d26cc8";
         sha256 = "1ibw27s352c2si22y209q17api8gaqv7qsh70vh4wk9bfv1kgchx";
@@ -33,7 +37,7 @@ let
 
       setupHook = ./../tool/setup-hooks.sh;
 
-      depsBuildBuild = with nixpkgs.buildPackages; [ llvm pkgconfig tup ];
+      depsBuildBuild = with buildPackages; [ llvm pkgconfig tup ];
 
       configurePhase = ''
         # Configure Tup
@@ -94,8 +98,11 @@ let
     };
 
 in rec {
-  base = buildRepo "base" [ ];
-  base-linux = buildRepo "base-linux" [ base ];
-  base-nova = buildRepo "base-nova" [ base ];
-  os = buildRepo "os" [ base ];
+  base = buildRepo "base";
+  base-linux = (buildRepo "base-linux").overrideAttrs
+    (attrs: { nativeBuildInputs = [ base ]; });
+  base-nova = (buildRepo "base-nova").overrideAttrs
+    (attrs: { nativeBuildInputs = [ base ]; });
+  os =
+    (buildRepo "os").overrideAttrs (attrs: { nativeBuildInputs = [ base ]; });
 }