diff --git a/src/Avalonia.Base/Styling/StyleInstance.cs b/src/Avalonia.Base/Styling/StyleInstance.cs
index e56d09838a..5823f76cec 100644
--- a/src/Avalonia.Base/Styling/StyleInstance.cs
+++ b/src/Avalonia.Base/Styling/StyleInstance.cs
@@ -45,7 +45,12 @@ namespace Avalonia.Styling
         public void Add(ISetterInstance instance)
         {
             if (instance is IValueEntry valueEntry)
-                base.Add(valueEntry);
+            {
+                if (Contains(valueEntry.Property))
+                    throw new InvalidOperationException(
+                        $"Duplicate setter encountered for property '{valueEntry.Property}' in '{Source}'.");
+                Add(valueEntry);
+            }
             else
                 (_setters ??= new()).Add(instance);
         }
diff --git a/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml b/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml
index 836cc27db3..26c3cd87f3 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml
@@ -53,7 +53,6 @@
 
   <!--  ButtonSpinner  -->
   <Style Selector="ButtonSpinner">
-    <Setter Property="Background" Value="Transparent" />
     <Setter Property="Foreground" Value="{DynamicResource TextControlForeground}" />
     <Setter Property="Padding" Value="10, 0" />
     <Setter Property="Background" Value="{DynamicResource TextControlBackground}" />