diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 05c4d582..e87e44c7 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -13,7 +13,7 @@ jobs:
         os: [ubuntu-latest, macos-latest, windows-latest]
         python-version: ["3.10", "3.11"]
 
-    runs-on: ${{ matrix.os }}
+    runs-on: ${ { matrix.os } }
 
     # a job is a seq of steps
     steps: