diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5c55825..0687ea3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -93,8 +93,7 @@ jobs:
               - g++-8
           - toolset: gcc-9
             cxxstd: "03,11,14,17,2a"
-            os: ubuntu-latest
-            container: ubuntu:18.04
+            os: ubuntu-20.04
             install:
               - g++-9
           - toolset: gcc-10