diff --git a/.azurepipelines/templates/pr-gate-steps.yml b/.azurepipelines/templates/pr-gate-steps.yml
index c1c0c04d6c..70c19a4621 100644
--- a/.azurepipelines/templates/pr-gate-steps.yml
+++ b/.azurepipelines/templates/pr-gate-steps.yml
@@ -31,6 +31,12 @@ steps:
     echo "##vso[task.setvariable variable=pkgs_to_build]${{ parameters.build_pkgs }}"
     echo "##vso[task.setvariable variable=pkg_count]${{ 1 }}"
 
+# Fetch the target branch so that pr_eval can diff them.
+# Seems like azure pipelines/github changed checkout process in nov 2020.
+- script: git fetch origin $(System.PullRequest.targetBranch)
+  displayName: fetch target branch
+  condition: eq(variables['Build.Reason'], 'PullRequest')
+
 # trim the package list if this is a PR
 - task: CmdLine@1
   displayName: Check if ${{ parameters.build_pkgs }} need testing