diff --git a/PiwigoDirectorySync/Services/FileIndexer.cs b/PiwigoDirectorySync/Services/FileIndexer.cs
index 386c131..18d3b89 100644
--- a/PiwigoDirectorySync/Services/FileIndexer.cs
+++ b/PiwigoDirectorySync/Services/FileIndexer.cs
@@ -1,4 +1,5 @@
-using System.Threading.Channels;
+using System.Collections.Concurrent;
+using System.Threading.Channels;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
@@ -9,9 +10,10 @@ namespace PiwigoDirectorySync.Services;
 
 internal class FileIndexer : IFileIndexer
 {
-    private readonly IList<string> _failedFiles = new List<string>();
+    private readonly ConcurrentBag<string> _failedFiles = new();
     private readonly ILogger<FileIndexer> _logger;
     private readonly IServiceProvider _serviceProvider;
+    private int _totalFilesScanned;
 
     public FileIndexer(ILogger<FileIndexer> logger, IServiceProvider serviceProvider)
     {
@@ -19,8 +21,9 @@ internal class FileIndexer : IFileIndexer
         _serviceProvider = serviceProvider;
     }
 
-    public int TotalFilesScanned { get; private set; }
-    public IReadOnlyCollection<string> FailedFiles => _failedFiles.AsReadOnly();
+    public int TotalFilesScanned => _totalFilesScanned;
+
+    public IReadOnlyCollection<string> FailedFiles => _failedFiles;
 
     public async Task StartProcessingAsync(Channel<string> fileQueue, int piwigoServerId, CancellationToken ct)
     {
@@ -74,7 +77,7 @@ internal class FileIndexer : IFileIndexer
 
             await db.SaveChangesAsync(ct);
 
-            TotalFilesScanned++;
+            Interlocked.Add(ref _totalFilesScanned, 1);
         }
         catch (Exception ex)
         {