diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 161878b9..10347cd3 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -13,7 +13,7 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04  # Downgrade Ubuntu to 20.04 to fix missing Python 3.6
     strategy:
       matrix:
         python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11"]