diff --git a/eng/common/scripts/Generate-PR-Diff.ps1 b/eng/common/scripts/Generate-PR-Diff.ps1
index 5c3d764009fe3..0ed03bb90da97 100644
--- a/eng/common/scripts/Generate-PR-Diff.ps1
+++ b/eng/common/scripts/Generate-PR-Diff.ps1
@@ -28,7 +28,7 @@ function Get-ChangedServices
     [string[]] $ChangedFiles
   )
 
-  $changedServices = $ChangedFiles | Foreach-Object { if ($_ -match "sdk/([^/]+)") { $matches[1] } } | Sort-Object -Unique
+  [string[]] $changedServices = $ChangedFiles | Foreach-Object { if ($_ -match "sdk/([^/]+)") { $matches[1] } } | Sort-Object -Unique
 
   return $changedServices
 }