diff --git a/.github/workflows/ci-freestanding.yml b/.github/workflows/ci-freestanding.yml
index 8f0cd3d9..ffdf5af5 100644
--- a/.github/workflows/ci-freestanding.yml
+++ b/.github/workflows/ci-freestanding.yml
@@ -131,8 +131,8 @@ jobs:
         shell: bash
         run: |
           conan build . -b missing -c tools.cmake.cmaketoolchain:generator="Ninja Multi-Config" \
-                        -c user.mp-units.build:all=True \
-                        -o '&:cxx_modules=${{ matrix.config.cxx_modules }}' -o '&:std_format=${{ env.std_format }}' -o '&:contracts=${{ matrix.contracts }}' ${{ matrix.config.conan-config }}
+                        -c user.mp-units.build:all=True -c tools.build:cxxflags="['-ffreestanding']" \
+                        -o '&:cxx_modules=${{ matrix.config.cxx_modules }}' -o '&:std_format=${{ env.std_format }}' -o '&:contracts=${{ matrix.contracts }}' -o '&:freestanding=True' ${{ matrix.config.conan-config }}
       - name: Clean Conan cache before backup
         shell: bash
         run: |