diff --git a/src/Microsoft.DotNet.Wpf/src/Shared/System/Windows/Markup/RuntimeIdentifierPropertyAttribute.cs b/src/Microsoft.DotNet.Wpf/src/Shared/System/Windows/Markup/RuntimeIdentifierPropertyAttribute.cs
index d65f78a6aee..92c3447394b 100644
--- a/src/Microsoft.DotNet.Wpf/src/Shared/System/Windows/Markup/RuntimeIdentifierPropertyAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/Shared/System/Windows/Markup/RuntimeIdentifierPropertyAttribute.cs
@@ -35,7 +35,7 @@ namespace System.Windows.Markup
     public sealed class RuntimeNamePropertyAttribute: Attribute
     {
         /// <summary/>
-        public RuntimeNamePropertyAttribute(string name)
+        public RuntimeNamePropertyAttribute(string? name)
         {
             Name = name;
         }
@@ -45,7 +45,7 @@ public RuntimeNamePropertyAttribute(string name)
         /// the class, this property needs to be of type string and have
         /// both get and set access
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
     }
 #endif
 
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/AcceptedMarkupExtensionExpressionTypeAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/AcceptedMarkupExtensionExpressionTypeAttribute.cs
index d0f6c2f84b8..4c6ad703eab 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/AcceptedMarkupExtensionExpressionTypeAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/AcceptedMarkupExtensionExpressionTypeAttribute.cs
@@ -2,17 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 namespace System.Windows.Markup
 {
     [Obsolete("This is not used by the XAML parser. Please look at XamlSetMarkupExtensionAttribute.")]
     [AttributeUsage(AttributeTargets.Class, AllowMultiple=true, Inherited=true)]
     public class AcceptedMarkupExtensionExpressionTypeAttribute: Attribute
     {
-        public Type Type { get; set; }
+        public Type? Type { get; set; }
 
-        public AcceptedMarkupExtensionExpressionTypeAttribute(Type type)
+        public AcceptedMarkupExtensionExpressionTypeAttribute(Type? type)
         {
             Type = type;
         }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ConstructorArgumentAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ConstructorArgumentAttribute.cs
index 16bfa7df788..110d07ed4f1 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ConstructorArgumentAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ConstructorArgumentAttribute.cs
@@ -19,7 +19,7 @@ public sealed class ConstructorArgumentAttribute : Attribute
         /// Constructor for an ConstructorArgumentAttribute
         /// </summary>
         /// <param name="argumentName">Name of the constructor argument that will initialize this property</param>
-        public ConstructorArgumentAttribute(string argumentName)
+        public ConstructorArgumentAttribute(string? argumentName)
         {
             ArgumentName = argumentName;
         }
@@ -27,6 +27,6 @@ public ConstructorArgumentAttribute(string argumentName)
         /// <summary>
         /// Name of the constructor argument that will initialize this property
         /// </summary>
-        public string ArgumentName { get; }
+        public string? ArgumentName { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ContentWrapperAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ContentWrapperAttribute.cs
index 5482c209626..8cb17decf1c 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ContentWrapperAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/ContentWrapperAttribute.cs
@@ -20,7 +20,7 @@ public sealed class ContentWrapperAttribute : Attribute
         /// type this attribute is declared on.
         /// </summary>
         /// <param name="contentWrapper"></param>
-        public ContentWrapperAttribute(Type contentWrapper)
+        public ContentWrapperAttribute(Type? contentWrapper)
         {
             ContentWrapper = contentWrapper;
         }
@@ -29,7 +29,7 @@ public ContentWrapperAttribute(Type contentWrapper)
         /// The type that is declared as a content wrapper for the collection type
         /// this attribute is declared on.
         /// </summary>
-        public Type ContentWrapper { get; }
+        public Type? ContentWrapper { get; }
 
         /// <summary>
         /// Override to ensure AttributeCollection perserves all instances
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DependsOnAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DependsOnAttribute.cs
index e7ad948b8a5..2ad392826f8 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DependsOnAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DependsOnAttribute.cs
@@ -23,7 +23,7 @@ public sealed class DependsOnAttribute : Attribute
         /// Constructor for DependsOnAttribute
         /// </summary>
         /// <param name="name">The name of the property that the property depends on</param>
-        public DependsOnAttribute(string name)
+        public DependsOnAttribute(string? name)
         {
             Name = name;
         }
@@ -36,6 +36,6 @@ public DependsOnAttribute(string name)
         /// <summary>
         /// The name of the property that is declared to depend on
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DictionaryKeyPropertyAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DictionaryKeyPropertyAttribute.cs
index 7fd216cef67..17f10facca7 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DictionaryKeyPropertyAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/DictionaryKeyPropertyAttribute.cs
@@ -10,11 +10,11 @@ namespace System.Windows.Markup
     [TypeForwardedFrom("WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")]
     public sealed class DictionaryKeyPropertyAttribute : Attribute
     {
-        public DictionaryKeyPropertyAttribute(string name)
+        public DictionaryKeyPropertyAttribute(string? name)
         {
             Name = name;
         }
 
-        public string Name { get; }
+        public string? Name { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/NameScopePropertyAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/NameScopePropertyAttribute.cs
index 6b9d8e18017..d8fbca69361 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/NameScopePropertyAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/NameScopePropertyAttribute.cs
@@ -10,17 +10,17 @@ namespace System.Windows.Markup
     [TypeForwardedFrom("WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")]
     public sealed class NameScopePropertyAttribute : Attribute
     {
-        public NameScopePropertyAttribute(string name)
+        public NameScopePropertyAttribute(string? name)
         {
             Name = name;
         }
 
-        public NameScopePropertyAttribute(string name, Type? type) : this(name)
+        public NameScopePropertyAttribute(string? name, Type? type) : this(name)
         {
             Type = type;
         }
 
-        public string Name { get; }
+        public string? Name { get; }
         public Type? Type { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/RootNamespaceAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/RootNamespaceAttribute.cs
index 02f41706264..f7f1f0e69cb 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/RootNamespaceAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/RootNamespaceAttribute.cs
@@ -19,7 +19,7 @@ public sealed class RootNamespaceAttribute : Attribute
         /// RootNamespace property in a project file.
         /// </summary>
         /// <param name="nameSpace">The root namespace value</param>
-        public RootNamespaceAttribute(string nameSpace)
+        public RootNamespaceAttribute(string? nameSpace)
         {
             Namespace = nameSpace;
         }
@@ -28,6 +28,6 @@ public RootNamespaceAttribute(string nameSpace)
         /// The root namespace value corresponding to the value of the RootNamespace
         /// property in a project file.
         /// </summary>
-        public string Namespace { get; }
+        public string? Namespace { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/UidPropertyAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/UidPropertyAttribute.cs
index 1fcc2ef0f6a..187d205ef44 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/UidPropertyAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/UidPropertyAttribute.cs
@@ -27,7 +27,7 @@ public sealed class UidPropertyAttribute : Attribute
         /// Creates a new UidPropertyAttribute with the given string as
         /// the property name.
         /// </summary>
-        public UidPropertyAttribute(string name)
+        public UidPropertyAttribute(string? name)
         {
             Name = name;
         }
@@ -35,6 +35,6 @@ public UidPropertyAttribute(string name)
         /// <summary>
         /// The name of the property that is designated to accept the x:Uid value
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetMarkupExtensionAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetMarkupExtensionAttribute.cs
index 877eab81bd9..79a92d2478d 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetMarkupExtensionAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetMarkupExtensionAttribute.cs
@@ -7,11 +7,11 @@ namespace System.Windows.Markup
     [AttributeUsage(AttributeTargets.Class, Inherited=true, AllowMultiple=false)]
     public sealed class XamlSetMarkupExtensionAttribute : Attribute
     {
-        public XamlSetMarkupExtensionAttribute(string xamlSetMarkupExtensionHandler)
+        public XamlSetMarkupExtensionAttribute(string? xamlSetMarkupExtensionHandler)
         {
             XamlSetMarkupExtensionHandler = xamlSetMarkupExtensionHandler;
         }
 
-        public string XamlSetMarkupExtensionHandler { get; }
+        public string? XamlSetMarkupExtensionHandler { get; }
     }
 }
diff --git a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetTypeConverterAttribute.cs b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetTypeConverterAttribute.cs
index 4da1de3254d..74a88f06020 100644
--- a/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetTypeConverterAttribute.cs
+++ b/src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Windows/Markup/XamlSetTypeConverterAttribute.cs
@@ -7,11 +7,11 @@ namespace System.Windows.Markup
    [AttributeUsage(AttributeTargets.Class, Inherited = true, AllowMultiple = false)]
     public sealed class XamlSetTypeConverterAttribute : Attribute
     {
-        public XamlSetTypeConverterAttribute(string xamlSetTypeConverterHandler)
+        public XamlSetTypeConverterAttribute(string? xamlSetTypeConverterHandler)
         {
             XamlSetTypeConverterHandler = xamlSetTypeConverterHandler;
         }
 
-        public string XamlSetTypeConverterHandler { get; }
+        public string? XamlSetTypeConverterHandler { get; }
     }
 }