diff --git a/.gitea/workflows/deploy.yaml b/.gitea/workflows/deploy.yaml
index 8a2615f..40ef588 100644
--- a/.gitea/workflows/deploy.yaml
+++ b/.gitea/workflows/deploy.yaml
@@ -14,6 +14,15 @@ jobs:
         with:
           node-version: "22"
 
+      # setup-node installs Node but not Yarn. GitHub's hosted images happen to
+      # ship Yarn preinstalled, so this workflow was silently depending on the
+      # image rather than on anything declared here — and broke the moment the
+      # act_runner image changed, with `yarn: command not found` (exit 127).
+      # Pin to 1.x: the lockfile is v1 format and `--frozen-lockfile` is v1
+      # syntax (v2+ renamed it `--immutable`).
+      - name: Install Yarn
+        run: npm install -g yarn@1
+
       - name: Install dependencies
         run: yarn install --frozen-lockfile