diff --git a/.github/workflows/phpunit.yml b/.github/workflows/phpunit.yml
index a241592..658eb82 100644
--- a/.github/workflows/phpunit.yml
+++ b/.github/workflows/phpunit.yml
@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.operating-system }}
     strategy:
       matrix:
-        operating-system: ['ubuntu-18.04']
+        operating-system: ['ubuntu-20.04']
         php-versions: ['7.2', '7.3', '7.4', '8.0']
 
     steps: