diff --git a/.config/project/default.nix b/.config/project/default.nix
index 9f6b027..7dcf60a 100644
--- a/.config/project/default.nix
+++ b/.config/project/default.nix
@@ -40,6 +40,9 @@
   programs = {
     treefmt = {
       enable = true;
+      ## NB: Treefmt 2 formats “hidden” files, which are ignored by the default
+      ##     version. See numtide/treefmt-nix#228.
+      package = pkgs.treefmt2;
       ## NB: This is normally "flake.nix", but since this repo contains
       ##     sub-flakes, we pick a random file that is unlikely to exist
       ##     anywhere else in the tree (and we can’t use .git/config, because it
diff --git a/flake.lock b/flake.lock
index fd0d0e0..7e39fbd 100644
--- a/flake.lock
+++ b/flake.lock
@@ -103,11 +103,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1728072441,
-        "narHash": "sha256-frEKgAV04sLvQl9ZbD4FyQK/TbSXdabiF5Xai8YrM8w=",
+        "lastModified": 1729530158,
+        "narHash": "sha256-rprj2S6w8RjDyNPnHbb2HIgE8lnbfic8L1YbUURJRYU=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "c8257f4524ee5863ee3421508e8b9ed500decf48",
+        "rev": "a3f90277d366596f8fdac8d9608d2471e204a77a",
         "type": "github"
       },
       "original": {
@@ -167,11 +167,11 @@
     },
     "nixpkgs-unstable": {
       "locked": {
-        "lastModified": 1728031656,
-        "narHash": "sha256-JXumn7X+suKEcehp4rchSvBzIboqyybQ5bLK4wk7gQU=",
+        "lastModified": 1729265718,
+        "narHash": "sha256-4HQI+6LsO3kpWTYuVGIzhJs1cetFcwT7quWCk/6rqeo=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "eeeb90a1dd3c9bea3afdbc76fd34d0fb2a727c7a",
+        "rev": "ccc0c2126893dd20963580b6478d1a10a4512185",
         "type": "github"
       },
       "original": {
@@ -204,14 +204,19 @@
         "nixpkgs-23_05": "nixpkgs-23_05",
         "nixpkgs-23_11": "nixpkgs-23_11",
         "nixpkgs-unstable": "nixpkgs-unstable",
+        "systems": [
+          "project-manager",
+          "flaky",
+          "systems"
+        ],
         "treefmt-nix": "treefmt-nix"
       },
       "locked": {
-        "lastModified": 1728076820,
-        "narHash": "sha256-21nIXCH2WC/kjMXdQmYA+1w3Z4yrPwgaRs60L2JKv44=",
+        "lastModified": 1729562990,
+        "narHash": "sha256-dKDPMp8v604Rg5Z4vOEN71jp7r8nNMEqm3rSTkJAlQ8=",
         "owner": "sellout",
         "repo": "project-manager",
-        "rev": "060b679d2d65c1adcd22319e18262da4154851a1",
+        "rev": "287e442cb19b845fc4d6e112975fb7de4c37d229",
         "type": "github"
       },
       "original": {
@@ -270,11 +275,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1727984844,
-        "narHash": "sha256-xpRqITAoD8rHlXQafYZOLvUXCF6cnZkPfoq67ThN0Hc=",
+        "lastModified": 1729242555,
+        "narHash": "sha256-6jWSWxv2crIXmYSEb3LEVsFkCkyVHNllk61X4uhqfCs=",
         "owner": "numtide",
         "repo": "treefmt-nix",
-        "rev": "4446c7a6fc0775df028c5a3f6727945ba8400e64",
+        "rev": "d986489c1c757f6921a48c1439f19bfb9b8ecab5",
         "type": "github"
       },
       "original": {