diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 515e62f..f06eb01 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -71,9 +71,11 @@ jobs:
           - { compiler: clang-10,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04 }
           - { compiler: clang-11,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04 }
           - { compiler: clang-12,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04 }
-          - { compiler: clang-12,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04, install: 'clang-12 libc++-12-dev libc++abi-12-dev', stdlib: libc++ }
+            # libc++
+          - { compiler: clang-6.0, cxxstd: '03,11,14',       os: ubuntu-18.04, stdlib: libc++, install: 'clang-6.0 libc++-dev libc++abi-dev' }
+          - { compiler: clang-12,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04, stdlib: libc++, install: 'clang-12 libc++-12-dev libc++abi-12-dev' }
           - { name: Clang w/ sanitizers, sanitize: yes,
-              compiler: clang-12,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04, install: 'clang-12 libc++-12-dev libc++abi-12-dev', stdlib: libc++ }
+              compiler: clang-12,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04, stdlib: libc++, install: 'clang-12 libc++-12-dev libc++abi-12-dev' }
 
           # OSX, clang
           - { compiler: clang,     cxxstd: '03,11,14,17,2a', os: macos-10.15, sanitize: yes }