diff --git a/uSync.BackOffice/Services/SyncFileService.cs b/uSync.BackOffice/Services/SyncFileService.cs
index cd4663c3..b9836e0a 100644
--- a/uSync.BackOffice/Services/SyncFileService.cs
+++ b/uSync.BackOffice/Services/SyncFileService.cs
@@ -6,6 +6,8 @@
 using System.Xml.Linq;
 using System.Xml.Serialization;
 
+using Examine;
+
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 
@@ -504,8 +506,18 @@ public IEnumerable<OrderedNodeInfo> MergeFolders(string[] folders, string extens
 
             var items = GetFolderItems(absPath, extension);
 
+            var localKeys = new List<Guid>();
+
             foreach (var item in items)
             {
+				var itemKey = item.Value.Node.GetKey();
+				if (localKeys.Contains(itemKey))
+				{
+					throw new Exception($"Duplicate: Item key {itemKey} already exists for {item.Key} - run uSync Health check for more info.");
+				}
+				
+                localKeys.Add(itemKey);
+
                 if (trackerBase is not null && elements.TryGetValue(item.Key, out var value))
                 {
                     // merge these files.