diff --git a/.forgejo/workflows/validate.yml b/.forgejo/workflows/validate.yml
index d73ceef..e01288d 100644
--- a/.forgejo/workflows/validate.yml
+++ b/.forgejo/workflows/validate.yml
@@ -5,17 +5,23 @@ on:
   pull_request:
     branches: [main]
 
+# The repository uses the sha256 git object format. Git < 2.42 cannot speak
+# the sha256 wire protocol, so we must run the job in a container whose Debian
+# base has a recent-enough git (bookworm ships 2.39, trixie ships 2.47+).
 jobs:
   json-schema:
     name: JSON Schema (ajv)
     runs-on: ubuntu-latest
+    container:
+      image: node:24-trixie-slim
     steps:
-      - name: Install prerequisites in container
+      - name: Install git + curl in container
         run: |
           set -euo pipefail
-          command -v curl >/dev/null || { apt-get update && apt-get install -y curl ca-certificates; }
+          apt-get update
+          apt-get install -y --no-install-recommends git curl ca-certificates
+          git --version
           node --version
-          npm --version
 
       - name: Checkout
         uses: actions/checkout@v4
@@ -61,11 +67,15 @@ jobs:
   rego:
     name: Rego (opa fmt + opa test)
     runs-on: ubuntu-latest
+    container:
+      image: debian:trixie-slim
     steps:
-      - name: Install prerequisites in container
+      - name: Install git + curl in container
         run: |
           set -euo pipefail
-          command -v curl >/dev/null || { apt-get update && apt-get install -y curl ca-certificates; }
+          apt-get update
+          apt-get install -y --no-install-recommends git curl ca-certificates
+          git --version
 
       - name: Checkout
         uses: actions/checkout@v4