diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index adb2518..e21dd7b 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -37,6 +37,9 @@ jobs:
 
     name: build and test (os=${{ matrix.os }})
     runs-on: ${{ matrix.os }}
+    defaults:
+      run:
+        shell: bash
     steps:
       - name: Install Micromamba
         run: |