diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 8c3bf1eda..e286d279d 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -56,6 +56,7 @@ jobs:
             -D MSGPACK_BUILD_TESTS=ON \
             -D CMAKE_BUILD_TYPE=Debug \
             -D MSGPACK_GEN_COVERAGE=ON \
+            -D MSGPACK_USE_STD_VARIANT_ADAPTOR=ON \
             -D CMAKE_PREFIX_PATH="$HOME/zlib-prefix/64;$HOME/boost-prefix/64" \
             -B build \
             -S . || exit 1
diff --git a/.github/workflows/gha.yml b/.github/workflows/gha.yml
index 1fbb5ebc5..29fd31bf8 100644
--- a/.github/workflows/gha.yml
+++ b/.github/workflows/gha.yml
@@ -145,6 +145,7 @@ jobs:
           3)
             export CXX="g++-10"
             export MSGPACK_CXX_VERSION="MSGPACK_CXX17=ON"
+            export MSGPACK_USE_STD_VARIANT_ADAPTOR="MSGPACK_USE_STD_VARIANT_ADAPTOR=ON"
             ;;
           4)
             export CXX="clang++-10"
diff --git a/ci/build_cmake.sh b/ci/build_cmake.sh
index a89c44641..b6ad78c50 100755
--- a/ci/build_cmake.sh
+++ b/ci/build_cmake.sh
@@ -21,6 +21,7 @@ cmake \
     -D MSGPACK_CHAR_SIGN=${CHAR_SIGN} \
     -D MSGPACK_DEFAULT_API_VERSION=${API_VERSION} \
     -D MSGPACK_USE_X3_PARSE=${X3_PARSE} \
+    -D MSGPACK_USE_STD_VARIANT_ADAPTOR=${STD_VARIANT_ADAPTOR} \
     -D CMAKE_CXX_FLAGS="${CXXFLAGS} ${ARCH_FLAG}" \
     -D CMAKE_INSTALL_PREFIX=$prefix_dir \
     -B $build_dir \