diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f6e73a2..7cf1d5b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -92,13 +92,14 @@ jobs:
             install: clang-7
           - toolset: clang
             compiler: clang++-8
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "03,11,14,17"
             os: ubuntu-20.04
             install: clang-8
           - toolset: clang
             compiler: clang++-9
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-20.04
+            install: clang-9
           - toolset: clang
             compiler: clang++-10
             cxxstd: "03,11,14,17,2a"