diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3845c9c3..e379dbe2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,6 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        os: [ ubuntu-20.04,  macos-13 ]
         smalltalk: [ 3.5.3, 3.5.8, 3.6.0, 3.6.4, 3.6.5, 3.6.6, 3.7.0 ]
         include:
           - smalltalk: 3.7.0