diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 964c2103..71e94942 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -7,13 +7,13 @@ on:
 
 jobs:
   rspec:
-    name: rspec (${{ matrix.ruby-version }}, ${{ matrix.os }}, shard ${{ matrix.shard }})
-    timeout-minutes: ${{ matrix.os == 'windows' && 30 || 15 }}
-    runs-on: ${{ format('{0}-latest', matrix.os) }}
+    name: rspec (${{ matrix.ruby-version }}, ${{ matrix.target.os }}, shard ${{ matrix.target.shard }}/${{ matrix.target.shards }})
+    timeout-minutes: ${{ matrix.target.os == 'windows' && 30 || 15 }}
+    runs-on: ${{ format('{0}-latest', matrix.target.os) }}
     env:
       BUNDLE_WITHOUT: lint
-      SPEC_WORKERS: ${{ matrix.os == 'windows' && 4 || 8 }}
-      SPEC_SHARD: ${{ matrix.shard }}
+      SPEC_WORKERS: ${{ matrix.target.os == 'windows' && 4 || 8 }}
+      SPEC_SHARD: ${{ matrix.target.shard }}/${{ matrix.target.shards }}
 
     strategy:
       fail-fast: false
@@ -22,10 +22,13 @@ jobs:
           - "3.3"
           - "3.4"
           - "4.0"
-        os:
-          - ubuntu
-          - windows
-        shard: ["1/3", "2/3", "3/3"]
+        target:
+          - { os: ubuntu, shard: 1, shards: 1 }
+          - { os: windows, shard: 1, shards: 5 }
+          - { os: windows, shard: 2, shards: 5 }
+          - { os: windows, shard: 3, shards: 5 }
+          - { os: windows, shard: 4, shards: 5 }
+          - { os: windows, shard: 5, shards: 5 }
 
     steps:
       - uses: actions/checkout@v4
@@ -56,7 +59,7 @@ jobs:
         uses: coverallsapp/github-action@v2
         with:
           github-token: ${{ secrets.github_token }}
-          flag-name: ruby${{ matrix.ruby-version }}-${{ matrix.os }}-shard${{ strategy.job-index }}
+          flag-name: ruby${{ matrix.ruby-version }}-${{ matrix.target.os }}-shard${{ matrix.target.shard }}of${{ matrix.target.shards }}
           parallel: true
 
   overcommit:
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 83dfc146..80900ef9 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -46,7 +46,7 @@ The best way to see a feature added, however, is to submit a pull request.
   # Optionally choose the number of worker processes (default: up to 8 CPUs):
   SPEC_WORKERS=4 bundle exec ruby script/parallel_rspec.rb
   # Run one runner's share of the suite (default: 1/1, the whole suite):
-  SPEC_SHARD=1/3 bundle exec ruby script/parallel_rspec.rb
+  SPEC_SHARD=1/5 bundle exec ruby script/parallel_rspec.rb
   ```
 
   Workers run in separate processes because specs change the working directory
@@ -56,6 +56,8 @@ The best way to see a feature added, however, is to submit a pull request.
   You can also pass spec paths to run a subset. The `lint` dependency group is
   only needed for lint checks; test-only CI jobs install with `BUNDLE_WITHOUT=lint`.
 
+  GitHub Actions runs one Linux shard and five Windows shards per Ruby version.
+
   The final `CI` check depends on all test shards and lint, and finalizes coverage reporting.
   Repository rulesets can require this single check instead of individual matrix jobs.
 
diff --git a/spec/spec_shard_spec.rb b/spec/spec_shard_spec.rb
index 258fc606..f5e0d853 100644
--- a/spec/spec_shard_spec.rb
+++ b/spec/spec_shard_spec.rb
@@ -9,7 +9,7 @@
     described_class.new('1/1').select(examples).should == examples
   end
 
-  [2, 3].each do |total|
+  [2, 3, 5].each do |total|
     context "with #{total} shards" do
       let(:shards) do
         (1..total).map { |index| described_class.new("#{index}/#{total}").select(examples) }