diff --git a/.github/workflows/gem_push.yml b/.github/workflows/gem_push.yml
index 9e55104..f04f617 100644
--- a/.github/workflows/gem_push.yml
+++ b/.github/workflows/gem_push.yml
@@ -26,9 +26,11 @@ jobs:
       - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
-          ruby-version: ruby
+          # Sigstore signing fails on Ruby 4.0, whose json 3 rejects options
+          # that protobug 0.1.0 passes to JSON.parse. Use 3.4 until it's fixed.
+          ruby-version: '3.4'
           bundler-cache: true
-      - uses: rubygems/configure-rubygems-credentials@v1.0.0
+      - uses: rubygems/configure-rubygems-credentials@v2.1.0
       - name: Update RubyGems
         run: gem update --system
       - name: Build gem