diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1e396be6..9ff442e2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -58,6 +58,7 @@ jobs:
         shell: ${{ contains(matrix.image, 'windows') && 'msys2 {0}' || 'bash' }}
     env:
       CC: ${{ !contains(matrix.image, 'windows') && 'clang' || '' }}
+      old-cmake-version: 3.11.4
     strategy:
       fail-fast: false
       matrix:
@@ -75,18 +76,33 @@ jobs:
             mingw-w64-x86_64-zlib mingw-w64-x86_64-libgcrypt mingw-w64-x86_64-openssl mingw-w64-x86_64-mbedtls
 
       - name: 'install packages'
-        if: ${{ !contains(matrix.image, 'windows') }}
         run: |
-          if [[ '${{ matrix.image }}' = *'ubuntu'* ]]; then
+          if [[ '${{ matrix.image }}' = *'windows'* ]]; then
+            cd "${HOME}" || exit 1
+            curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 60 --retry 3 --retry-connrefused \
+              --location 'https://github.com/Kitware/CMake/releases/download/v${{ env.old-cmake-version }}/cmake-${{ env.old-cmake-version }}-win64-x64.zip' --output bin.zip
+            unzip -q bin.zip
+            rm -f bin.zip
+            printf '%s' "${HOME}/cmake-${{ env.old-cmake-version }}-win64-x64/bin/cmake.exe" > "${HOME}/old-cmake-path.txt"
+          elif [[ '${{ matrix.image }}' = *'ubuntu'* ]]; then
             sudo rm -f /var/lib/man-db/auto-update
             sudo apt-get -o Dpkg::Use-Pty=0 install libgcrypt-dev libssl-dev libmbedtls-dev libwolfssl-dev
+            cd "${HOME}" || exit 1
+            curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 60 --retry 3 --retry-connrefused \
+              --location https://github.com/Kitware/CMake/releases/download/v${{ env.old-cmake-version }}/cmake-${{ env.old-cmake-version }}-Linux-x86_64.tar.gz | tar -xzf -
+            printf '%s' "$PWD/cmake-${{ env.old-cmake-version }}-Linux-x86_64/bin/cmake" > "${HOME}/old-cmake-path.txt"
           else
             brew install libgcrypt openssl mbedtls wolfssl
+            cd "${HOME}" || exit 1
+            curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 60 --retry 3 --retry-connrefused \
+              --location https://github.com/Kitware/CMake/releases/download/v${{ env.old-cmake-version }}/cmake-${{ env.old-cmake-version }}-Darwin-x86_64.tar.gz | tar -xzf -
+            printf '%s' "$PWD/cmake-${{ env.old-cmake-version }}-Darwin-x86_64/CMake.app/Contents/bin/cmake" > "${HOME}/old-cmake-path.txt"
           fi
 
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
         with:
           persist-credentials: false
+
       - name: 'via FetchContent'
         run: ./tests/cmake/test.sh FetchContent
       - name: 'via add_subdirectory OpenSSL'
@@ -103,6 +119,26 @@ jobs:
         if: ${{ !contains(matrix.image, 'windows') }}  # MSYS2 wolfSSL package not built with the OpenSSL compatibility option
         run: ./tests/cmake/test.sh find_package -DCRYPTO_BACKEND=wolfSSL
 
+      - name: 'via add_subdirectory OpenSSL (old cmake)'
+        run: |
+          export TEST_CMAKE_CONSUMER="$(cat "${HOME}/old-cmake-path.txt")"
+          [[ '${{ matrix.image }}' = *'macos'* ]] && export CFLAGS='-arch arm64'
+          if [[ '${{ matrix.image }}' = *'windows'* ]]; then
+            export TEST_CMAKE_GENERATOR='MSYS Makefiles'
+            export TEST_CMAKE_FLAGS='-DCMAKE_C_COMPILER=x86_64-w64-mingw32-gcc -DOPENSSL_ROOT_DIR=C:/msys64/mingw64'
+          fi
+          ./tests/cmake/test.sh add_subdirectory -DCRYPTO_BACKEND=OpenSSL ${options}
+
+      - name: 'via find_package OpenSSL (old cmake)'
+        run: |
+          export TEST_CMAKE_CONSUMER="$(cat "${HOME}/old-cmake-path.txt")"
+          [[ '${{ matrix.image }}' = *'macos'* ]] && export CFLAGS='-arch arm64'
+          if [[ '${{ matrix.image }}' = *'windows'* ]]; then
+            export TEST_CMAKE_GENERATOR='MSYS Makefiles'
+            export TEST_CMAKE_FLAGS='-DCMAKE_C_COMPILER=x86_64-w64-mingw32-gcc -DOPENSSL_ROOT_DIR=C:/msys64/mingw64'
+          fi
+          ./tests/cmake/test.sh find_package -DCRYPTO_BACKEND=OpenSSL ${options}
+
   build_linux:
     name: 'linux'
     runs-on: ubuntu-latest
diff --git a/tests/cmake/test.sh b/tests/cmake/test.sh
index 247d8148..dadb5808 100755
--- a/tests/cmake/test.sh
+++ b/tests/cmake/test.sh
@@ -9,17 +9,25 @@ set -eu
 
 cd "$(dirname "$0")"
 
-command -v ninja >/dev/null && export CMAKE_GENERATOR=Ninja  # 3.17+
-
 mode="${1:-all}"; shift
 
-cmake_consumer="${CMAKE_CONSUMER:-cmake}"
-cmake_provider="${CMAKE_PROVIDER:-${cmake_consumer}}"
+cmake_consumer="${TEST_CMAKE_CONSUMER:-cmake}"
+cmake_provider="${TEST_CMAKE_PROVIDER:-${cmake_consumer}}"
 
 # 'modern': supports -S/-B (3.13+), --install (3.15+)
 "${cmake_consumer}" --help | grep -q -- '--install' && cmake_consumer_modern=1
 "${cmake_provider}" --help | grep -q -- '--install' && cmake_provider_modern=1
 
+if [ -n "${TEST_CMAKE_GENERATOR:-}" ]; then
+  gen="${TEST_CMAKE_GENERATOR}"
+elif [ -n "${cmake_consumer_modern:-}" ] && \
+     [ -n "${cmake_provider_modern:-}" ] && \
+     command -v ninja >/dev/null; then
+  gen='Ninja'  # 3.17+
+else
+  gen='Unix Makefiles'
+fi
+
 cmake_opts='-DBUILD_EXAMPLES=OFF -DBUILD_TESTING=OFF -DENABLE_ZLIB_COMPRESSION=ON'
 
 src='../..'
@@ -28,7 +36,7 @@ runresults() {
   set +x
   for bin in "$1"/test-consumer*; do
     file "${bin}" || true
-    ${LIBSSH2_TEST_EXE_RUNNER:-} "${bin}" || true
+    ${TEST_CMAKE_EXE_RUNNER:-} "${bin}" || true
   done
   set -x
 }
@@ -40,13 +48,13 @@ if [ "${mode}" = 'ExternalProject' ]; then  # Broken
   bldc='bld-externalproject'
   rm -rf "${bldc}"
   if [ -n "${cmake_consumer_modern:-}" ]; then  # 3.15+
-    "${cmake_consumer}" -B "${bldc}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON "$@" \
+    "${cmake_consumer}" -B "${bldc}" -G "${gen}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON ${TEST_CMAKE_FLAGS:-} "$@" \
       -DTEST_INTEGRATION_MODE=ExternalProject \
       -DFROM_ARCHIVE="${src}" -DFROM_HASH="${sha}"
     "${cmake_consumer}" --build "${bldc}" --verbose
   else
     mkdir "${bldc}"; cd "${bldc}"
-    "${cmake_consumer}" .. ${cmake_opts} "$@" \
+    "${cmake_consumer}" .. -G "${gen}" ${cmake_opts} ${TEST_CMAKE_FLAGS:-} "$@" \
       -DTEST_INTEGRATION_MODE=ExternalProject \
       -DFROM_ARCHIVE="${src}" -DFROM_HASH="${sha}"
     VERBOSE=1 "${cmake_consumer}" --build .
@@ -59,7 +67,7 @@ if [ "${mode}" = 'all' ] || [ "${mode}" = 'FetchContent' ]; then  # 3.14+
   src="${PWD}/${src}"
   bldc='bld-fetchcontent'
   rm -rf "${bldc}"
-  "${cmake_consumer}" -B "${bldc}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON "$@" \
+  "${cmake_consumer}" -B "${bldc}" -G "${gen}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON ${TEST_CMAKE_FLAGS:-} "$@" \
     -DTEST_INTEGRATION_MODE=FetchContent \
     -DFROM_GIT_REPO="${src}" \
     -DFROM_GIT_TAG="$(git rev-parse HEAD)"
@@ -76,14 +84,14 @@ if [ "${mode}" = 'all' ] || [ "${mode}" = 'add_subdirectory' ]; then
   bldc='bld-add_subdirectory'
   rm -rf "${bldc}"
   if [ -n "${cmake_consumer_modern:-}" ]; then  # 3.15+
-    "${cmake_consumer}" -B "${bldc}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON "$@" \
+    "${cmake_consumer}" -B "${bldc}" -G "${gen}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON ${TEST_CMAKE_FLAGS:-} "$@" \
       -DTEST_INTEGRATION_MODE=add_subdirectory
     "${cmake_consumer}" --build "${bldc}" --verbose
   else
     mkdir "${bldc}"; cd "${bldc}"
     # Disable `pkg-config` for CMake <= 3.12. These versions cannot propagate
     # library directories to the consumer project.
-    "${cmake_consumer}" .. ${cmake_opts} -DLIBSSH2_USE_PKGCONFIG=OFF "$@" \
+    "${cmake_consumer}" .. -G "${gen}" ${cmake_opts} -DLIBSSH2_USE_PKGCONFIG=OFF ${TEST_CMAKE_FLAGS:-} "$@" \
       -DTEST_INTEGRATION_MODE=add_subdirectory
     VERBOSE=1 "${cmake_consumer}" --build .
     cd ..
@@ -98,28 +106,28 @@ if [ "${mode}" = 'all' ] || [ "${mode}" = 'find_package' ]; then
   prefix="${PWD}/${bldp}/_pkg"
   rm -rf "${bldp}"
   if [ -n "${cmake_provider_modern:-}" ]; then  # 3.15+
-    "${cmake_provider}" -B "${bldp}" -S "${src}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON "$@" \
+    "${cmake_provider}" -B "${bldp}" -S "${src}" -G "${gen}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON ${TEST_CMAKE_FLAGS:-} "$@" \
       -DCMAKE_INSTALL_PREFIX="${prefix}"
-    "${cmake_provider}" --build "${bldp}"
+    "${cmake_provider}" --build "${bldp}" --verbose
     "${cmake_provider}" --install "${bldp}"
   else
     mkdir "${bldp}"; cd "${bldp}"
-    "${cmake_provider}" "${src}" ${cmake_opts} "$@" \
+    "${cmake_provider}" "${src}" -G "${gen}" ${cmake_opts} ${TEST_CMAKE_FLAGS:-} "$@" \
       -DCMAKE_INSTALL_PREFIX="${prefix}"
-    "${cmake_provider}" --build .
+    VERBOSE=1 "${cmake_provider}" --build .
     make install
     cd ..
   fi
   bldc='bld-find_package'
   rm -rf "${bldc}"
   if [ -n "${cmake_consumer_modern:-}" ]; then  # 3.15+
-    "${cmake_consumer}" -B "${bldc}" \
+    "${cmake_consumer}" -B "${bldc}" -G "${gen}" ${TEST_CMAKE_FLAGS:-} \
       -DTEST_INTEGRATION_MODE=find_package \
       -DCMAKE_PREFIX_PATH="${prefix}/lib/cmake/libssh2"
     "${cmake_consumer}" --build "${bldc}" --verbose
   else
     mkdir "${bldc}"; cd "${bldc}"
-    "${cmake_consumer}" .. \
+    "${cmake_consumer}" .. -G "${gen}" ${TEST_CMAKE_FLAGS:-} \
       -DTEST_INTEGRATION_MODE=find_package \
       -DCMAKE_PREFIX_PATH="${prefix}/lib/cmake/libssh2"
     VERBOSE=1 "${cmake_consumer}" --build .