diff --git a/src/Avalonia.Controls/SplitButton/ToggleSplitButton.cs b/src/Avalonia.Controls/SplitButton/ToggleSplitButton.cs
index 83bc9851c1..fd7ea28ba1 100644
--- a/src/Avalonia.Controls/SplitButton/ToggleSplitButton.cs
+++ b/src/Avalonia.Controls/SplitButton/ToggleSplitButton.cs
@@ -18,7 +18,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Raised when the <see cref="IsChecked"/> property value changes.
         /// </summary>
-        public event EventHandler<RoutedEventArgs> IsCheckedChanged
+        public event EventHandler<RoutedEventArgs>? IsCheckedChanged
         {
             add => AddHandler(IsCheckedChangedEvent, value);
             remove => RemoveHandler(IsCheckedChangedEvent, value);