diff --git a/configs/nixos/modules/shell/fish/config.fish b/configs/nixos/modules/shell/fish/config.fish
index 08d8b9e..cc687be 100644
--- a/configs/nixos/modules/shell/fish/config.fish
+++ b/configs/nixos/modules/shell/fish/config.fish
@@ -3,6 +3,8 @@ set -g fish_key_bindings fish_vi_key_bindings
 
 set -gx EDITOR nvim
 set -gx VISUAL nvim
+# TODO: source this from a shell toolchain registry.
+set -gx RUST_TOOLCHAIN_ROOT /nix/store/ph2z7wfzcxyrl1y0349dzcjkas3bifhw-rust-toolchain
 
 # Render man pages through bat.
 set -x MANROFFOPT "-c"