diff --git a/devenv.lock b/devenv.lock
index 33cc56ad7..7bc5cbec8 100644
--- a/devenv.lock
+++ b/devenv.lock
@@ -110,6 +110,22 @@
       }
     },
     "nixpkgs-stable": {
+      "locked": {
+        "lastModified": 1699291058,
+        "narHash": "sha256-5ggduoaAMPHUy4riL+OrlAZE14Kh7JWX4oLEs22ZqfU=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "41de143fda10e33be0f47eab2bfe08a50f234267",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-23.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-stable_2": {
       "locked": {
         "lastModified": 1685801374,
         "narHash": "sha256-otaSUoFEMM+LjBI1XL/xGB5ao6IwnZOXc47qhIgJe8U=",
@@ -133,7 +149,7 @@
         "nixpkgs": [
           "nixpkgs"
         ],
-        "nixpkgs-stable": "nixpkgs-stable"
+        "nixpkgs-stable": "nixpkgs-stable_2"
       },
       "locked": {
         "lastModified": 1699271226,
@@ -154,6 +170,7 @@
         "devenv": "devenv",
         "fenix": "fenix",
         "nixpkgs": "nixpkgs",
+        "nixpkgs-stable": "nixpkgs-stable",
         "pre-commit-hooks": "pre-commit-hooks"
       }
     },
diff --git a/devenv.nix b/devenv.nix
index 1fb24adc4..bc9fdba1c 100644
--- a/devenv.nix
+++ b/devenv.nix
@@ -1,15 +1,22 @@
-{ pkgs, lib, config, ... }:
-
+{ pkgs, lib, config, inputs, ... }:
+let
+  pkgs-stable = import inputs.nixpkgs-stable { system = pkgs.stdenv.system; };
+in
 {
-  # https://devenv.sh/basics/
-
   # https://devenv.sh/packages/
   # on macos frameworks have to be explicitly specified 
   # otherwise a linker error ocurs on rust packages
-  packages = [pkgs.just] ++ lib.optionals pkgs.stdenv.isDarwin (with pkgs.darwin.apple_sdk; [
-    frameworks.CoreServices
-    frameworks.CoreFoundation
-  ]);
+  packages = [
+    pkgs.just
+    pkgs.llvmPackages_16.libllvm
+    # cargo-llvm-cov is currently marked broken on nixpkgs unstable
+    pkgs-stable.cargo-llvm-cov
+  ] ++ lib.optionals
+    pkgs.stdenv.isDarwin
+    (with pkgs.darwin.apple_sdk; [
+      frameworks.CoreServices
+      frameworks.CoreFoundation
+    ]);
 
   # https://devenv.sh/scripts/
   scripts.hello.exec = "echo Welcome to hugr dev shell!";
@@ -17,6 +24,8 @@
   enterShell = ''
     hello
     cargo --version
+    export LLVM_COV="${pkgs.llvmPackages_16.libllvm}/bin/llvm-cov"
+    export LLVM_PROFDATA="${pkgs.llvmPackages_16.libllvm}/bin/llvm-profdata"
   '';
 
   # https://devenv.sh/languages/
diff --git a/devenv.yaml b/devenv.yaml
index b8fc6397e..5a9261d03 100644
--- a/devenv.yaml
+++ b/devenv.yaml
@@ -1,4 +1,6 @@
 inputs:
+  nixpkgs-stable:
+    url: github:NixOS/nixpkgs/nixos-23.05
   fenix:
     url: github:nix-community/fenix
     inputs: