diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 2b3713e3e..8cbf3e4f5 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -69,6 +69,7 @@ jobs:
         run: |
           rm -rf ${{runner.workspace}}/boost_prebuild
           git clone --depth=1 https://github.com/BeamMW/boost_prebuild_${{matrix.os}}.git ${{runner.workspace}}/boost_prebuild
+          echo "BOOST_ROOT=${{runner.workspace}}/boost_prebuild" >> $GITHUB_ENV
           echo "BOOST_INCLUDEDIR=${{runner.workspace}}/boost_prebuild/include" >> $GITHUB_ENV
           echo "BOOST_LIBRARYDIR=${{runner.workspace}}/boost_prebuild/lib/" >> $GITHUB_ENV