diff --git a/eng/common/scripts/New-RegenerateMatrix.ps1 b/eng/common/scripts/New-RegenerateMatrix.ps1
index 63d1f228e101..c876ed1f64e2 100644
--- a/eng/common/scripts/New-RegenerateMatrix.ps1
+++ b/eng/common/scripts/New-RegenerateMatrix.ps1
@@ -6,11 +6,15 @@ param (
   [Parameter()]
   [string]$OutputVariableName,
 
+  # Both counts are used as divisors when splitting the items, so reject zero and
+  # negative values here rather than failing later with a divide-by-zero.
   [Parameter()]
+  [ValidateRange(1, [int]::MaxValue)]
   [int]$JobCount = 8,
 
   # The minimum number of items per job. If the number of items is less than this, then the number of jobs will be reduced.
   [Parameter()]
+  [ValidateRange(1, [int]::MaxValue)]
   [int]$MinimumPerJob = 10,
 
   [Parameter()]
@@ -40,7 +44,11 @@ function Split-Items([array]$Items) {
   }
   
   $itemsPerGroup = [math]::Floor($itemCount / $JobCount)
-  $largeJobCount = $itemCount % $itemsPerGroup
+  # The remainder has to be taken over the number of groups, not the size of a group.
+  # Taking it over $itemsPerGroup produces too few large groups whenever
+  # $itemCount % $itemsPerGroup -lt $itemCount % $JobCount, and the trailing items are
+  # then silently dropped from the matrix.
+  $largeJobCount = $itemCount % $JobCount
   $groups = [object[]]::new($JobCount)
 
   $i = 0