diff --git a/nukebuild/RefAssemblyGenerator.cs b/nukebuild/RefAssemblyGenerator.cs
index 5c5324ac8f..61cb04c438 100644
--- a/nukebuild/RefAssemblyGenerator.cs
+++ b/nukebuild/RefAssemblyGenerator.cs
@@ -39,10 +39,13 @@ public class RefAssemblyGenerator
             ProcessType(nested, obsoleteCtor);
         if (type.IsInterface)
         {
-            var hideMethods = type.Name.EndsWith("Impl");
+            var hideMethods = type.Name.EndsWith("Impl")
+                              || (type.HasCustomAttributes && type.CustomAttributes.Any(a =>
+                                  a.AttributeType.FullName == "Avalonia.Metadata.PrivateApiAttribute"));
+
             var injectMethod = hideMethods
                                || type.CustomAttributes.Any(a =>
-                                   a.AttributeType.FullName.EndsWith("NotClientImplementableAttribute"));
+                                   a.AttributeType.FullName == "Avalonia.Metadata.NotClientImplementableAttribute");
             
             if (hideMethods)
             {
@@ -65,7 +68,7 @@ public class RefAssemblyGenerator
             }
 
             var forceUnstable = type.CustomAttributes.Any(a =>
-                a.AttributeType.FullName.EndsWith("UnstableAttribute"));
+                a.AttributeType.FullName == "Avalonia.Metadata.UnstableAttribute");
             
             foreach (var m in type.Methods)
                 MarkAsUnstable(m, obsoleteCtor, forceUnstable);
@@ -81,11 +84,10 @@ public class RefAssemblyGenerator
     {
         if (!force
             || def.HasCustomAttributes == false
-            || !def.CustomAttributes.Any(a =>
-                a.AttributeType.FullName.EndsWith("UnstableAttribute")))
+            || def.CustomAttributes.All(a => a.AttributeType.FullName != "Avalonia.Metadata.UnstableAttribute"))
             return;
-        
-        if (def.CustomAttributes.Any(a => a.TypeFullName.EndsWith("ObsoleteAttribute")))
+
+        if (def.CustomAttributes.Any(a => a.TypeFullName == "System.ObsoleteAttribute"))
             return;
 
         def.CustomAttributes.Add(new CustomAttribute(obsoleteCtor, new CAArgument[]
diff --git a/src/Avalonia.Base/Metadata/PrivateApiAttribute.cs b/src/Avalonia.Base/Metadata/PrivateApiAttribute.cs
new file mode 100644
index 0000000000..3f60940c5e
--- /dev/null
+++ b/src/Avalonia.Base/Metadata/PrivateApiAttribute.cs
@@ -0,0 +1,9 @@
+using System;
+
+namespace Avalonia.Metadata;
+
+[AttributeUsage(AttributeTargets.Interface)]
+public sealed class PrivateApiAttribute : Attribute
+{
+
+}
\ No newline at end of file
diff --git a/src/Avalonia.Base/Platform/ICursorFactory.cs b/src/Avalonia.Base/Platform/ICursorFactory.cs
index fff1f92d53..99a9a9d7fa 100644
--- a/src/Avalonia.Base/Platform/ICursorFactory.cs
+++ b/src/Avalonia.Base/Platform/ICursorFactory.cs
@@ -1,9 +1,11 @@
 using Avalonia.Input;
+using Avalonia.Metadata;
 
 #nullable enable
 
 namespace Avalonia.Platform
 {
+    [PrivateApi]
     public interface ICursorFactory
     {
         ICursorImpl GetCursor(StandardCursorType cursorType);
diff --git a/src/Avalonia.Base/Platform/IPlatformRenderInterface.cs b/src/Avalonia.Base/Platform/IPlatformRenderInterface.cs
index 81fe2c046f..6f62c3be1d 100644
--- a/src/Avalonia.Base/Platform/IPlatformRenderInterface.cs
+++ b/src/Avalonia.Base/Platform/IPlatformRenderInterface.cs
@@ -11,7 +11,7 @@ namespace Avalonia.Platform
     /// <summary>
     /// Defines the main platform-specific interface for the rendering subsystem.
     /// </summary>
-    [Unstable]
+    [Unstable, PrivateApi]
     public interface IPlatformRenderInterface
     {
         /// <summary>
@@ -201,7 +201,7 @@ namespace Avalonia.Platform
         bool IsSupportedBitmapPixelFormat(PixelFormat format);
     }
 
-    [Unstable]
+    [Unstable, PrivateApi]
     public interface IPlatformRenderInterfaceContext : IOptionalFeatureProvider, IDisposable
     {
         /// <summary>
diff --git a/src/Avalonia.Controls/Platform/IPlatformIconLoader.cs b/src/Avalonia.Controls/Platform/IPlatformIconLoader.cs
index 4c844ce30f..2ff74cc582 100644
--- a/src/Avalonia.Controls/Platform/IPlatformIconLoader.cs
+++ b/src/Avalonia.Controls/Platform/IPlatformIconLoader.cs
@@ -3,7 +3,7 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Platform
 {
-    [Unstable]
+    [Unstable, PrivateApi]
     public interface IPlatformIconLoader
     {
         IWindowIconImpl LoadIcon(string fileName);
diff --git a/src/Avalonia.Controls/Platform/IWindowingPlatform.cs b/src/Avalonia.Controls/Platform/IWindowingPlatform.cs
index 5acc5adccd..f6cf8c604e 100644
--- a/src/Avalonia.Controls/Platform/IWindowingPlatform.cs
+++ b/src/Avalonia.Controls/Platform/IWindowingPlatform.cs
@@ -2,7 +2,7 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Platform
 {
-    [Unstable]
+    [Unstable, PrivateApi]
     public interface IWindowingPlatform
     {
         IWindowImpl CreateWindow();