diff --git a/.github/workflows/core.yml b/.github/workflows/core.yml
index 6257376a..445e6e0e 100644
--- a/.github/workflows/core.yml
+++ b/.github/workflows/core.yml
@@ -7,7 +7,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
+        os: [ubuntu-20.04, windows-latest, macos-latest]
         python-version: ["3.6", "3.9", "3.11"]
 
     runs-on: ${{ matrix.os }}