diff --git a/README.md b/README.md
index 7923bb7..a796f64 100644
--- a/README.md
+++ b/README.md
@@ -25,3 +25,4 @@ Add this to your repository's `renovate.json`:
 | Patch automerge | Enabled | Patch updates auto-merge after checks pass |
 | GitHub Actions automerge | Minor and patch only | Minor and patch Actions updates auto-merge; major requires manual review |
 | Vulnerability exemption | 0 seconds | Security remediation PRs bypass the 3-day quarantine |
+| Go module tidy | `gomodTidy` | Renovate runs `go mod tidy` after Go module updates so stale `go.sum` entries are pruned instead of accumulating |
diff --git a/default.json b/default.json
index 0474079..33b3185 100644
--- a/default.json
+++ b/default.json
@@ -19,6 +19,7 @@
     "automerge": true,
     "commitMessageAction": "lock file maintenance"
   },
+  "postUpdateOptions": ["gomodTidy"],
   "packageRules": [
     {
       "description": "Keep krypsis-io/.github shared workflows on main, never pin",