diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d00f6bd08c..838344f10f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,7 +38,7 @@ jobs:
       - name: Generate CI matrix
         id: generate-matrix
         run: |
-          brew ruby -- "$(brew --repository homebrew/cask)/cmd/lib/generate-matrix.rb" "${{ github.event.pull_request.url }}"
+          brew ruby -- "$(brew --repository homebrew/cask)/cmd/lib/generate-matrix.rb" --url="${{ github.event.pull_request.url }}"
 
   test:
     name: ${{ matrix.name }}