diff --git a/.azure-pipelines/templates/steps/tox-steps.yml b/.azure-pipelines/templates/steps/tox-steps.yml
index 9cb84aa3a..4267d7bbf 100644
--- a/.azure-pipelines/templates/steps/tox-steps.yml
+++ b/.azure-pipelines/templates/steps/tox-steps.yml
@@ -41,7 +41,7 @@ steps:
       ln -s $(testFarmPem.secureFilePath) tests/letstest/test-farm.pem
     condition: contains(variables['TOXENV'], 'test-farm')
   - bash: |
-      export TARGET_BRANCH="${BUILD_SOURCEBRANCH/refs\/(heads|tags)\//}"
+      export TARGET_BRANCH="${BUILD_SOURCEBRANCH/refs\\/(heads|tags)\\//}"
       [ -z "${SYSTEM_PULLREQUEST_TARGETBRANCH}" ] || export TARGET_BRANCH="${SYSTEM_PULLREQUEST_TARGETBRANCH}"
       env
       if [[ "${TOXENV}" == *"oldest"* ]]; then