diff --git a/CHANGELOG.md b/CHANGELOG.md
index dceec6a9c..419c03e45 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+- Saving a key from Provider Settings works again on Macs where Nix or
+  Homebrew coreutils sit ahead of `/bin` on `PATH`. The credential hardener
+  now spawns Apple's `/bin/chmod -N` by absolute path; GNU `chmod` has no `-N`,
+  so the ACL strip failed closed and every save was refused (Arthur Bogaart, #694).
+
 - Render on iPad and iPhone instead of stopping with "An error occurred while
   rendering." Cesium's per-vertex model atmosphere binds shader `out`
   parameters directly to varyings, which Apple's Metal/ANGLE backend cannot
diff --git a/server/standalone/key-setup-hardening.mjs b/server/standalone/key-setup-hardening.mjs
index 002ccabdc..78440948c 100644
--- a/server/standalone/key-setup-hardening.mjs
+++ b/server/standalone/key-setup-hardening.mjs
@@ -123,7 +123,11 @@ export function hardenCredentialFile(
   if (platform !== 'win32') {
     try {
       if (platform === 'darwin') {
-        const aclRemoval = spawn('chmod', ['-N', filepath], {
+        // `-N` (strip the ACL) is Apple-only. Spawn /bin/chmod by absolute
+        // path, never by name: a Nix/Homebrew coreutils profile puts GNU chmod
+        // first on PATH, and GNU chmod rejects `-N` — which was treated as a
+        // hardening failure and refused every save on such machines.
+        const aclRemoval = spawn('/bin/chmod', ['-N', filepath], {
           stdio: 'ignore',
         });
         if (!commandCompletedSuccessfully(aclRemoval)) return false;
diff --git a/src/keySetupHardening.test.mjs b/src/keySetupHardening.test.mjs
index 2578be37d..c519576e3 100644
--- a/src/keySetupHardening.test.mjs
+++ b/src/keySetupHardening.test.mjs
@@ -55,6 +55,21 @@ test('macOS ACL removal failure stops before chmod and fails closed', () => {
   assert.deepEqual(fileSystem.calls, [], 'mode bits must not disguise an ACL-removal failure');
 });
 
+test('macOS ACL removal spawns Apple /bin/chmod by absolute path, not via PATH', () => {
+  const spawned = [];
+  hardenCredentialFile(FILE, {
+    platform: 'darwin',
+    fileSystem: fileSystemWithMode(0o100600),
+    spawn(command, args) {
+      spawned.push([command, args]);
+      return { status: 0, signal: null };
+    },
+  });
+  // A coreutils-first PATH (Nix home-manager, Homebrew) resolves bare `chmod`
+  // to GNU chmod, which has no `-N` and would fail every save.
+  assert.deepEqual(spawned, [['/bin/chmod', ['-N', FILE]]]);
+});
+
 test('POSIX hardening verifies the resulting 0600 mode', () => {
   const goodFs = fileSystemWithMode(0o100600);
   assert.equal(hardenCredentialFile(FILE, {