diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 1991b25259..131c386089 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -103,9 +103,10 @@ jobs:
       run: |
            sudo apt update
            sudo apt install clang-13
+           sudo apt install libc++-dev
       shell: bash
     - name: cmake
-      run: cmake -S . -B build -DJSONCONS_SANITIZE=ON -DCMAKE_BUILD_TYPE=Debug -DJSONCONS_BUILD_TESTS=On -DCMAKE_CXX_STANDARD=20 -DCMAKE_CXX_STANDARD_REQUIRED=ON
+      run: cmake -S . -B build -DJSONCONS_SANITIZE=ON -DCMAKE_BUILD_TYPE=Debug -DJSONCONS_BUILD_TESTS=On -DCMAKE_CXX_STANDARD=20 -DCMAKE_CXX_STANDARD_REQUIRED=ON -DCMAKE_CXX_FLAGS="-stdlib=libc++ -std=c++20"
       env:
         CC:   clang-13
         CXX:  clang++-13