diff --git a/.gitea/workflows/build-after-flake-update.yml b/.gitea/workflows/build-after-flake-update.yml
new file mode 100644
index 0000000..71c55f7
--- /dev/null
+++ b/.gitea/workflows/build-after-flake-update.yml
@@ -0,0 +1,29 @@
+name: Build (nix)
+
+on:
+  workflow_run:
+    workflows:
+      - Update flake lock
+    types:
+      - completed
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    if: ${{ gitea.event.workflow_run.conclusion == 'success' }}
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+        with:
+          # The update workflow may have pushed a newer flake.lock commit.
+          ref: ${{ gitea.event.workflow_run.head_branch }}
+
+      - name: Install upstream Nix
+        uses: cachix/install-nix-action@v31
+
+      - name: Build flake
+        run: nix build