diff --git a/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateMsiBase.cs b/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateMsiBase.cs
index 11b7560fa4b..fe351813b94 100644
--- a/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateMsiBase.cs
+++ b/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateMsiBase.cs
@@ -115,6 +115,11 @@ public string SuppressIces
         /// </summary>
         private readonly object extractNuGetLock = new object();
 
+        /// <summary>
+        /// Used to syncrhonize access to MSI task items.
+        /// </summary>
+        private readonly object msiTaskItemsLock = new();
+
         /// <summary>
         /// Generate a set of MSIs for the specified platforms using the specified NuGet package.
         /// </summary>
@@ -124,11 +129,16 @@ public string SuppressIces
         protected IEnumerable<ITaskItem> Generate(string sourcePackage, string swixPackageId, string outputPath, WorkloadPackKind kind, params string[] platforms)
         {
             NugetPackage nupkg = null;
+            List<TaskItem> msis = null;
+
             lock (extractNuGetLock)
             {
                 nupkg = new(sourcePackage, Log);
             }
-            List<TaskItem> msis = new();
+            lock (msiTaskItemsLock)
+            {
+                msis = new();
+            }
 
             // MSI ProductName defaults to the package title and fallback to the package ID with a warning.
             string productName = nupkg.Title;
@@ -310,7 +320,10 @@ protected IEnumerable<ITaskItem> Generate(string sourcePackage, string swixPacka
                 // Generate a .csproj to build a NuGet payload package to carry the MSI and JSON manifest
                 msi.SetMetadata(Metadata.PackageProject, GeneratePackageProject(msi.ItemSpec, msiJsonPath, platform, nupkg));
 
-                msis.Add(msi);
+                lock (msiTaskItemsLock)
+                {
+                    msis.Add(msi);
+                }
             });
 
             return msis;
diff --git a/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateWorkloadMsis.cs b/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateWorkloadMsis.cs
index 50340821555..6acc58554ed 100644
--- a/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateWorkloadMsis.cs
+++ b/src/Microsoft.DotNet.Build.Tasks.Workloads/src/GenerateWorkloadMsis.cs
@@ -45,11 +45,20 @@ public ITaskItem[] MissingPacks
             set;
         }
 
+        /// <summary>
+        /// Used for synchronizing on MSI task item.
+        /// </summary>
+        private readonly object msiTaskItemsLock = new();
+
         public override bool Execute()
         {
             try
             {
-                List<ITaskItem> msis = new();
+                List<ITaskItem> msis = null;
+                lock (msiTaskItemsLock)
+                {
+                    msis = new();
+                }
                 List<ITaskItem> missingPacks = new();
 
                 if (string.IsNullOrWhiteSpace(PackagesPath))
@@ -96,7 +105,12 @@ public override bool Execute()
 
                 System.Threading.Tasks.Parallel.ForEach(packsToGenerate, p =>
                 {
-                    msis.AddRange(Generate(p.sourcePackage, p.swixPackageId, p.outputPath, p.kind, p.platforms));
+                    var msiItems = Generate(p.sourcePackage, p.swixPackageId, p.outputPath, p.kind, p.platforms);
+
+                    lock (msiTaskItemsLock)
+                    {
+                        msis.AddRange(msiItems);
+                    }
                 });
 
                 Msis = msis.ToArray();