diff --git a/nix/base-system/flake.nix b/nix/base-system/flake.nix
index 7ec6e54..a87a734 100644
--- a/nix/base-system/flake.nix
+++ b/nix/base-system/flake.nix
@@ -146,6 +146,7 @@ EOF";
           zsh.interactiveShellInit = (builtins.readFile ./.zshrc);
         };
         environment.systemPackages = (with pkgs; [
+            isabelle
             texlive.combined.scheme-basic
             terraform # TODO(jeremy): Replace with opentofu when that is an option.
             terraform-ls
diff --git a/nix/darwin/flake.lock b/nix/darwin/flake.lock
index fbdb391..7282f67 100644
--- a/nix/darwin/flake.lock
+++ b/nix/darwin/flake.lock
@@ -37,11 +37,11 @@
       "locked": {
         "lastModified": 1,
         "narHash": "sha256-FpujwFIx2bubT7wtgYSHve+hlDoZBTO7DELMowAEeww=",
-        "path": "/nix/store/9ap10sma6dkx591mgh06698l34zyxmv6-source/nix/base-system",
+        "path": "/nix/store/hnmh4b4nmhqc3pmz1mymkl5w86xv9632-source/nix/base-system",
         "type": "path"
       },
       "original": {
-        "path": "/nix/store/9ap10sma6dkx591mgh06698l34zyxmv6-source/nix/base-system",
+        "path": "/nix/store/hnmh4b4nmhqc3pmz1mymkl5w86xv9632-source/nix/base-system",
         "type": "path"
       }
     },