diff --git a/README.md b/README.md
index 1f76e74..6299da5 100644
--- a/README.md
+++ b/README.md
@@ -53,7 +53,7 @@ jobs:
       contents: read
     steps:
       - uses: actions/checkout@v5.0.0
-      - uses: DeterminateSystems/determinate-nix-action@main # or v3.9.0 to pin to a release
+      - uses: DeterminateSystems/determinate-nix-action@main # or v3.9.1 to pin to a release
       - run: nix build .
 ```
 
@@ -67,10 +67,10 @@ jobs:
 Unlike `DeterminateSystems/nix-installer-action`, we fully support explicit version pinning for maximum consistency.
 This Action is **automatically tagged** for every Determinate Nix release, giving you complete control over your CI environment:
 
-📍 Pinning to `DeterminateSystems/determinate-nix-action@v3.9.0` guarantees:
+📍 Pinning to `DeterminateSystems/determinate-nix-action@v3.9.1` guarantees:
 
 - Same `nix-installer-action` revision every time
-- Consistent Determinate Nix v3.9.0 installation
+- Consistent Determinate Nix v3.9.1 installation
 - Reproducible CI workflows, even years later
 
 ✨ Using `@main` instead? You'll:
@@ -112,7 +112,7 @@ updates:
 | `source-branch`         | The branch of `nix-installer` to use (conflicts with `source-tag`, `source-revision`, `source-pr`)                                                                                                                                                                             |          |                            |
 | `source-pr`             | The PR of `nix-installer` to use (conflicts with `source-tag`, `source-revision`, `source-branch`)                                                                                                                                                                             |          |                            |
 | `source-revision`       | The revision of `nix-installer` to use (conflicts with `source-tag`, `source-branch`, `source-pr`)                                                                                                                                                                             |          |                            |
-| `source-tag`            | The tag of `nix-installer` to use (conflicts with `source-revision`, `source-branch`, `source-pr`)                                                                                                                                                                             |          | `v3.9.0`                   |
+| `source-tag`            | The tag of `nix-installer` to use (conflicts with `source-revision`, `source-branch`, `source-pr`)                                                                                                                                                                             |          | `v3.9.1`                   |
 | `source-url`            | A URL pointing to a `nix-installer` executable                                                                                                                                                                                                                                 |          |                            |
 | `backtrace`             | The setting for `RUST_BACKTRACE` (see https://doc.rust-lang.org/std/backtrace/index.html#environment-variables)                                                                                                                                                                |          |                            |
 | `diagnostic-endpoint`   | Diagnostic endpoint url where the installer sends data to. To disable set this to an empty string.                                                                                                                                                                             |          | `-`                        |
diff --git a/action.yml b/action.yml
index 4bfb04f..edfc5d4 100644
--- a/action.yml
+++ b/action.yml
@@ -68,7 +68,7 @@
         "source-tag": {
             "description": "The tag of `nix-installer` to use (conflicts with `source-revision`, `source-branch`, `source-pr`)",
             "required": false,
-            "default": "v3.9.0"
+            "default": "v3.9.1"
         },
         "source-url": {
             "description": "A URL pointing to a `nix-installer` executable",
diff --git a/flake.lock b/flake.lock
index 77477b5..a8acf51 100644
--- a/flake.lock
+++ b/flake.lock
@@ -2,12 +2,12 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1756125398,
-        "narHash": "sha256-XexyKZpf46cMiO5Vbj+dWSAXOnr285GHsMch8FBoHbc=",
-        "rev": "3b9f00d7a7bf68acd4c4abb9d43695afb04e03a5",
-        "revCount": 851350,
+        "lastModified": 1756266583,
+        "narHash": "sha256-cr748nSmpfvnhqSXPiCfUPxRz2FJnvf/RjJGvFfaCsM=",
+        "rev": "8a6d5427d99ec71c64f0b93d45778c889005d9c2",
+        "revCount": 852432,
         "type": "tarball",
-        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.851350%2Brev-3b9f00d7a7bf68acd4c4abb9d43695afb04e03a5/0198e4ae-49a1-775e-8b7c-803015cc6285/source.tar.gz"
+        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.852432%2Brev-8a6d5427d99ec71c64f0b93d45778c889005d9c2/0198ed0a-af20-7ff9-9fe3-8435302f9575/source.tar.gz"
       },
       "original": {
         "type": "tarball",
diff --git a/tools/state.json b/tools/state.json
index 13021de..8b8e47d 100644
--- a/tools/state.json
+++ b/tools/state.json
@@ -1,5 +1,5 @@
 {
   "nix_installer_action_revision": "428f3c64a3f56011a8bfb3044a519374aff8e7df",
-  "determinate_nix_tag": "v3.9.0",
+  "determinate_nix_tag": "v3.9.1",
   "checkout_action_tag": "v5.0.0"
 }