diff --git a/Source/TrackableEntities.Client/ChangeTrackingCollection.cs b/Source/TrackableEntities.Client/ChangeTrackingCollection.cs
index 653de6f7..c7ed4a3a 100644
--- a/Source/TrackableEntities.Client/ChangeTrackingCollection.cs
+++ b/Source/TrackableEntities.Client/ChangeTrackingCollection.cs
@@ -165,9 +165,8 @@ private void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
                         || entity.TrackingState == TrackingState.Modified)
                     {
                         if (entity.ModifiedProperties == null)
-                            entity.ModifiedProperties = new List<string>();
-                        if (!entity.ModifiedProperties.Contains(e.PropertyName))
-                            entity.ModifiedProperties.Add(e.PropertyName);
+                            entity.ModifiedProperties = new HashSet<string>();
+                        entity.ModifiedProperties.Add(e.PropertyName);
                     }
                 }
             }