diff --git a/default.nix b/default.nix
index 39a8ac4ee..e2c602b6a 100644
--- a/default.nix
+++ b/default.nix
@@ -1,7 +1,14 @@
-{ system ? "x86_64-genode", self ? { }, nixpkgs ? import <nixpkgs> {
-  localSystem = "x86_64-linux";
-  crossSystem = "x86_64-genode";
-} }:
+let
+  nixpkgsGit = builtins.fetchGit {
+    url = "https://gitea.c3d2.de/ehmry/nixpkgs.git";
+    ref = "genode";
+  };
+  pinnedNixpkgs = import nixpkgsGit {
+    localSystem = "x86_64-linux";
+    crossSystem = "x86_64-genode";
+  };
+
+in { system ? "x86_64-genode", self ? { }, nixpkgs ? pinnedNixpkgs }:
 let
   inherit (nixpkgs) stdenv buildPackages fetchgit llvmPackages;
 
diff --git a/shell.nix b/shell.nix
index 77586954e..70b8b8601 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1 +1,2 @@
 let pkgs = import ./default.nix { }; in pkgs.base
+  # Use the "base" repository build for our shell environment.