diff --git a/.envrc b/.envrc
index 3550a30f..09ae5f36 100755
--- a/.envrc
+++ b/.envrc
@@ -1 +1,3 @@
-use flake
+if command -v nix >/dev/null 2>&1; then
+  use flake
+fi
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 2b91b510..a706cff1 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -21,7 +21,7 @@ crates include browser assets and do not require Node.js.
 
 ### Optional: Nix dev shell
 
-If you have [Nix](https://nixos.org/download/) with flakes enabled, `nix develop` provides the tools above at the versions CI uses. With [direnv](https://direnv.net/), `direnv allow` enters the shell automatically when you enter the directory.
+If you have [Nix](https://nixos.org/download/) with flakes enabled, `nix develop` provides the tools above at the versions CI uses. With [direnv](https://direnv.net/), `direnv allow` enters the shell automatically when you enter the directory. When Nix is not installed, direnv leaves your environment unchanged.
 
 | Command | What it runs |
 | --- | --- |