diff --git a/build/stage-determine-changes.yml b/build/stage-determine-changes.yml
index e9df1022e..db74001cd 100644
--- a/build/stage-determine-changes.yml
+++ b/build/stage-determine-changes.yml
@@ -6,11 +6,10 @@ jobs:
   steps:
   - powershell: |
       # Determine the context of the build (PR or push) and set the target branch accordingly
-      $prTargetBranch = "$(System.PullRequest.TargetBranch)"
-      $isPR = -not [string]::IsNullOrWhiteSpace($prTargetBranch)
+      $isPR = "$(Build.Reason)" -eq "PullRequest"
 
       # Normalize the target branch name for PR builds or default to 'master' for push builds
-      $targetBranchName = $isPR ? $prTargetBranch -replace 'refs/heads/', '' : "master"
+      $targetBranchName = $isPR ? "$(System.PullRequest.TargetBranch)" -replace 'refs/heads/', '' : "master"
       Write-Host "Build context determined: $(if ($isPR) { 'Pull Request targeting ' + $targetBranchName } else { 'Push' })"
 
       # Fetch the target or default base branch and determine the merge base