diff --git a/src/SharpSync/SharpSync.csproj b/src/SharpSync/SharpSync.csproj
index 6e3df75..60b4e95 100644
--- a/src/SharpSync/SharpSync.csproj
+++ b/src/SharpSync/SharpSync.csproj
@@ -69,7 +69,7 @@
     <PackageReference Include="sqlite-net-pcl" Version="1.11.285" />
     <PackageReference Include="WebDav.Client" Version="2.9.0" />
     <PackageReference Include="SSH.NET" Version="2026.0.0" />
-    <PackageReference Include="AWSSDK.S3" Version="4.0.103.1" />
+    <PackageReference Include="AWSSDK.S3" Version="4.0.103.4" />
     <PackageReference Include="FluentFTP" Version="55.0.0" />
     <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="5.9.0" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="10.0.401" PrivateAssets="all" />
diff --git a/tests/SharpSync.Tests/Storage/FtpStorageTests.cs b/tests/SharpSync.Tests/Storage/FtpStorageTests.cs
index 5c9a367..01dcebf 100644
--- a/tests/SharpSync.Tests/Storage/FtpStorageTests.cs
+++ b/tests/SharpSync.Tests/Storage/FtpStorageTests.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using Microsoft.Extensions.Logging.Abstractions;
 using Oire.SharpSync.Tests.Fixtures;
 
@@ -539,8 +540,8 @@ public async Task WriteFileAsync_LargeFile_SupportsProgressReporting() {
         var content = new byte[15 * 1024 * 1024]; // 15MB (larger than default chunk size)
         new Random().NextBytes(content);
 
-        var progressEvents = new List<StorageProgressEventArgs>();
-        _storage.ProgressChanged += (sender, args) => progressEvents.Add(args);
+        var progressEvents = new ConcurrentQueue<StorageProgressEventArgs>();
+        _storage.ProgressChanged += (sender, args) => progressEvents.Enqueue(args);
 
         // Act
         using var stream = new MemoryStream(content);
@@ -566,8 +567,8 @@ public async Task ReadFileAsync_LargeFile_SupportsProgressReporting() {
         using var writeStream = new MemoryStream(content);
         await _storage.WriteFileAsync(filePath, writeStream);
 
-        var progressEvents = new List<StorageProgressEventArgs>();
-        _storage.ProgressChanged += (sender, args) => progressEvents.Add(args);
+        var progressEvents = new ConcurrentQueue<StorageProgressEventArgs>();
+        _storage.ProgressChanged += (sender, args) => progressEvents.Enqueue(args);
 
         // Act
         using var readStream = await _storage.ReadFileAsync(filePath);
diff --git a/tests/SharpSync.Tests/Storage/S3StorageTests.cs b/tests/SharpSync.Tests/Storage/S3StorageTests.cs
index 3bfcc0c..2f0ac7e 100644
--- a/tests/SharpSync.Tests/Storage/S3StorageTests.cs
+++ b/tests/SharpSync.Tests/Storage/S3StorageTests.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using Microsoft.Extensions.Logging.Abstractions;
 using Oire.SharpSync.Tests.Fixtures;
 
@@ -591,8 +592,8 @@ public async Task ProgressChanged_LargeFileUpload_RaisesEvents() {
         var content = new byte[12 * 1024 * 1024];
         new Random().NextBytes(content);
 
-        var progressEvents = new List<StorageProgressEventArgs>();
-        _storage.ProgressChanged += (sender, args) => progressEvents.Add(args);
+        var progressEvents = new ConcurrentQueue<StorageProgressEventArgs>();
+        _storage.ProgressChanged += (sender, args) => progressEvents.Enqueue(args);
 
         // Act
         using var stream = new MemoryStream(content);
@@ -624,8 +625,8 @@ public async Task ProgressChanged_LargeFileDownload_RaisesEvents() {
         using var stream = new MemoryStream(content);
         await _storage.WriteFileAsync(filePath, stream);
 
-        var progressEvents = new List<StorageProgressEventArgs>();
-        _storage.ProgressChanged += (sender, args) => progressEvents.Add(args);
+        var progressEvents = new ConcurrentQueue<StorageProgressEventArgs>();
+        _storage.ProgressChanged += (sender, args) => progressEvents.Enqueue(args);
 
         // Act
         using var readStream = await _storage.ReadFileAsync(filePath);
diff --git a/tests/SharpSync.Tests/Storage/SftpStorageTests.cs b/tests/SharpSync.Tests/Storage/SftpStorageTests.cs
index 87de47f..1f25352 100644
--- a/tests/SharpSync.Tests/Storage/SftpStorageTests.cs
+++ b/tests/SharpSync.Tests/Storage/SftpStorageTests.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using Microsoft.Extensions.Logging.Abstractions;
 using Oire.SharpSync.Tests.Fixtures;
 
@@ -717,8 +718,8 @@ public async Task ProgressChanged_LargeFile_RaisesEvents() {
         var largeContent = new byte[15 * 1024 * 1024]; // 15 MB (larger than chunk size)
         new Random().NextBytes(largeContent);
 
-        var progressEvents = new List<StorageProgressEventArgs>();
-        _storage.ProgressChanged += (sender, args) => progressEvents.Add(args);
+        var progressEvents = new ConcurrentQueue<StorageProgressEventArgs>();
+        _storage.ProgressChanged += (sender, args) => progressEvents.Enqueue(args);
 
         // Act
         using var stream = new MemoryStream(largeContent);