diff --git a/.github/workflows/validate-registries.yml b/.github/workflows/validate-registries.yml
index 96b747144c..f507116a11 100644
--- a/.github/workflows/validate-registries.yml
+++ b/.github/workflows/validate-registries.yml
@@ -13,6 +13,44 @@ on:
       - "apps/v4/registry/directory.json"
 
 jobs:
+  check-registry-sync:
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    name: Check registry sync
+    permissions:
+      contents: read
+      pull-requests: write
+    steps:
+      - name: Check changed files
+        id: changed
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          CHANGED_FILES=$(gh pr diff ${{ github.event.pull_request.number }} --repo ${{ github.repository }} --name-only)
+
+          DIRECTORY_CHANGED=false
+          REGISTRIES_CHANGED=false
+
+          if echo "$CHANGED_FILES" | grep -q "^apps/v4/registry/directory.json$"; then
+            DIRECTORY_CHANGED=true
+          fi
+
+          if echo "$CHANGED_FILES" | grep -q "^apps/v4/public/r/registries.json$"; then
+            REGISTRIES_CHANGED=true
+          fi
+
+          echo "directory_changed=$DIRECTORY_CHANGED" >> $GITHUB_OUTPUT
+          echo "registries_changed=$REGISTRIES_CHANGED" >> $GITHUB_OUTPUT
+
+      - name: Flag missing registries.json update
+        if: steps.changed.outputs.directory_changed == 'true' && steps.changed.outputs.registries_changed == 'false'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh pr edit ${{ github.event.pull_request.number }} --repo ${{ github.repository }} --add-label "registries: invalid"
+          gh pr comment ${{ github.event.pull_request.number }} --repo ${{ github.repository }} --body "can you run \`pnpm registry:build\` and commit the json files please?"
+          exit 1
+
   validate:
     runs-on: ubuntu-latest
     name: pnpm validate:registries