diff --git a/XmlSchemaClassGenerator.Tests/MemoryOutputWriter.cs b/XmlSchemaClassGenerator.Tests/MemoryOutputWriter.cs
index b9566417..a27d08c6 100644
--- a/XmlSchemaClassGenerator.Tests/MemoryOutputWriter.cs
+++ b/XmlSchemaClassGenerator.Tests/MemoryOutputWriter.cs
@@ -1,7 +1,9 @@
 using System.CodeDom;
 using System.Collections.Generic;
 using System.IO;
+using System.Runtime.Versioning;
 
+[assembly:UnsupportedOSPlatform("ios")]
 namespace XmlSchemaClassGenerator.Tests
 {
     internal class MemoryOutputWriter : OutputWriter
diff --git a/XmlSchemaClassGenerator/CodeUtilities.cs b/XmlSchemaClassGenerator/CodeUtilities.cs
index a267ed2f..f41b8b2e 100644
--- a/XmlSchemaClassGenerator/CodeUtilities.cs
+++ b/XmlSchemaClassGenerator/CodeUtilities.cs
@@ -1,6 +1,7 @@
 using System;
 using System.CodeDom;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Text.RegularExpressions;
 using System.Xml;
@@ -360,7 +361,7 @@ public static KeyValuePair<NamespaceKey, string> ParseNamespace(string nsArg, st
             return new KeyValuePair<NamespaceKey, string>(new NamespaceKey(source, xmlNs), netNs);
         }
 
-        public static readonly List<(string Namespace, Func<GeneratorConfiguration,bool> Condition)> UsingNamespaces = new() {
+        public static readonly ImmutableList<(string Namespace, Func<GeneratorConfiguration,bool> Condition)> UsingNamespaces = ImmutableList.Create<(string Namespace, Func<GeneratorConfiguration, bool> Condition)>(
             ("System", c => c.CompactTypeNames),
             ("System.CodeDom.Compiler", c => c.CompactTypeNames),
             ("System.Collections.Generic", c => c.CompactTypeNames),
@@ -372,7 +373,7 @@ public static KeyValuePair<NamespaceKey, string> ParseNamespace(string nsArg, st
             ("System.Xml", c => c.CompactTypeNames),
             ("System.Xml.Schema", c => c.CompactTypeNames),
             ("System.Xml.Serialization", c => c.CompactTypeNames)
-        };
+        );
 
         public static bool IsUsingNamespace(Type t, GeneratorConfiguration conf) => UsingNamespaces.Any(n => n.Namespace == t.Namespace && n.Condition(conf));
 
diff --git a/XmlSchemaClassGenerator/XmlSchemaClassGenerator.csproj b/XmlSchemaClassGenerator/XmlSchemaClassGenerator.csproj
index 2894a8c3..21442858 100644
--- a/XmlSchemaClassGenerator/XmlSchemaClassGenerator.csproj
+++ b/XmlSchemaClassGenerator/XmlSchemaClassGenerator.csproj
@@ -48,6 +48,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
+    <PackageReference Include="System.Collections.Immutable" Version="6.0.0" />
     <PackageReference Include="System.Text.Encoding.CodePages" Version="6.0.0" />
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>