diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 344da48..b048bd0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -84,8 +84,9 @@ jobs:
         if: "startsWith( matrix.os, 'windows-' )"
         shell: cmd
         run: |
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
           set BOOST_BRANCH=develop
-          if "%GITHUB_REF%" == "master" set BOOST_BRANCH=master
+          if "%GITHUB_BASE_REF%" == "master" set BOOST_BRANCH=master
           cd ..
           git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
           cd boost-root