diff --git a/.github/workflows/dotnet-core.yml b/.github/workflows/dotnet-core.yml
index 9088df9c..a2d9b187 100644
--- a/.github/workflows/dotnet-core.yml
+++ b/.github/workflows/dotnet-core.yml
@@ -183,12 +183,12 @@ jobs:
         name: nuget-package
         path: .libsodium-pack/bin/Release/libsodium.1.0.18.nupkg
 
-  test-ubuntu18_04:
+  test-ubuntu20_04:
     runs-on: ubuntu-latest
     needs:
     - pack
     container:
-      image: mcr.microsoft.com/dotnet/core/sdk:3.1-bionic
+      image: mcr.microsoft.com/dotnet/core/sdk:3.1-focal
     env:
       DOTNET_CLI_TELEMETRY_OPTOUT: 1
       DOTNET_SKIP_FIRST_TIME_EXPERIENCE: 1