diff --git a/RoslynPreviewSdkReferences.props b/RoslynPreviewSdkReferences.props
new file mode 100644
index 000000000..b33089fac
--- /dev/null
+++ b/RoslynPreviewSdkReferences.props
@@ -0,0 +1,19 @@
+<Project>
+  <PropertyGroup>
+    <RoslynPreviewSdkPath>/usr/share/dotnet/sdk/11.0.100-preview.5.26302.115/Roslyn/bincore</RoslynPreviewSdkPath>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'net10.0'">
+    <!--
+      DRAFT PR HACK: use the Roslyn bits from .NET 11 Preview 5 so CSharpier can
+      parse C# 15 closed/union syntax before matching NuGet packages are published.
+      Replace this import with Microsoft.CodeAnalysis.CSharp from NuGet once available.
+    -->
+    <Reference Include="Microsoft.CodeAnalysis">
+      <HintPath>$(RoslynPreviewSdkPath)/Microsoft.CodeAnalysis.dll</HintPath>
+    </Reference>
+    <Reference Include="Microsoft.CodeAnalysis.CSharp">
+      <HintPath>$(RoslynPreviewSdkPath)/Microsoft.CodeAnalysis.CSharp.dll</HintPath>
+    </Reference>
+  </ItemGroup>
+</Project>
diff --git a/Src/CSharpier.Cli/CSharpier.Cli.csproj b/Src/CSharpier.Cli/CSharpier.Cli.csproj
index a2f9b21a9..72828af41 100644
--- a/Src/CSharpier.Cli/CSharpier.Cli.csproj
+++ b/Src/CSharpier.Cli/CSharpier.Cli.csproj
@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="../../Nuget/Build.props" />
+  <Import Project="../../RoslynPreviewSdkReferences.props" />
   <PropertyGroup>
     <NoWarn>$(NoWarn);NU1510</NoWarn>
     <OutputType>Exe</OutputType>
diff --git a/Src/CSharpier.Core/CSharp/SyntaxPrinter/Modifiers.cs b/Src/CSharpier.Core/CSharp/SyntaxPrinter/Modifiers.cs
index f966d6084..05239d327 100644
--- a/Src/CSharpier.Core/CSharp/SyntaxPrinter/Modifiers.cs
+++ b/Src/CSharpier.Core/CSharp/SyntaxPrinter/Modifiers.cs
@@ -21,6 +21,7 @@ private class DefaultOrder : IComparer<SyntaxToken>
             "new",
             "virtual",
             "abstract",
+            "closed",
             "sealed",
             "override",
             "readonly",
diff --git a/Src/CSharpier.Core/CSharpier.Core.csproj b/Src/CSharpier.Core/CSharpier.Core.csproj
index 9edf84f98..c1f53d93a 100644
--- a/Src/CSharpier.Core/CSharpier.Core.csproj
+++ b/Src/CSharpier.Core/CSharpier.Core.csproj
@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="../../Nuget/Build.props" />
+  <Import Project="../../RoslynPreviewSdkReferences.props" />
   <PropertyGroup>
     <PackageId>CSharpier.Core</PackageId>
     <TargetFrameworks>net8.0;net9.0;net10.0;netstandard2.0</TargetFrameworks>
@@ -13,7 +14,6 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="LovettSoftware.XmlDiff" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" />
     <PackageReference Include="Microsoft.CodeAnalysis.PublicApiAnalyzers">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
@@ -24,6 +24,9 @@
     </PackageReference>
     <PackageReference Include="System.IO.Abstractions" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' != 'net10.0'">
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'net10.0'">
     <PackageReference Include="System.Text.Json" />
   </ItemGroup>
diff --git a/Src/CSharpier.Generators/NodePrinterGenerator.cs b/Src/CSharpier.Generators/NodePrinterGenerator.cs
index da37af63b..c33944122 100644
--- a/Src/CSharpier.Generators/NodePrinterGenerator.cs
+++ b/Src/CSharpier.Generators/NodePrinterGenerator.cs
@@ -74,6 +74,7 @@ public class NodePrinterGenerator : IIncrementalGenerator
                 nameof(SyntaxKind.RecordStructDeclaration),
                 nameof(SyntaxKind.EnumDeclaration),
                 nameof(SyntaxKind.ExtensionBlockDeclaration),
+                "(SyntaxKind)9082", // SyntaxKind.UnionDeclaration in .NET 11 Preview 5
             }
         },
         {
@@ -275,7 +276,12 @@ private object GetModel(ImmutableArray<SyntaxTree> syntaxTrees)
                 PrinterName = fileName,
                 SyntaxNodeName = $"{fileName}Syntax",
                 SyntaxKinds = SpecialCase.TryGetValue($"{fileName}Syntax", out var kinds)
-                    ? string.Join(" or ", kinds.Select(x => $"SyntaxKind.{x}"))
+                    ? string.Join(
+                        " or ",
+                        kinds.Select(x =>
+                            x.StartsWith("(", StringComparison.Ordinal) ? x : $"SyntaxKind.{x}"
+                        )
+                    )
                     : $"SyntaxKind.{fileName}",
             })
             .OrderBy(o => o.SyntaxNodeName)
diff --git a/Src/CSharpier.Tests/CSharpier.Tests.csproj b/Src/CSharpier.Tests/CSharpier.Tests.csproj
index 761bc5540..1dd22f205 100644
--- a/Src/CSharpier.Tests/CSharpier.Tests.csproj
+++ b/Src/CSharpier.Tests/CSharpier.Tests.csproj
@@ -1,4 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../../RoslynPreviewSdkReferences.props" />
   <PropertyGroup>
     <IsPackable>false</IsPackable>
     <RootNamespace>CSharpier.Tests</RootNamespace>
diff --git a/Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ClosedAndUnionModifiers.expected.test b/Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ClosedAndUnionModifiers.expected.test
new file mode 100644
index 000000000..381ae8956
--- /dev/null
+++ b/Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ClosedAndUnionModifiers.expected.test
@@ -0,0 +1,20 @@
+public closed record class JobStatus;
+
+public record class Queued : JobStatus;
+
+public record class Running(int PercentComplete) : JobStatus;
+
+public union Pet(Cat, Dog, Bird);
+
+public union Length(Meters, Feet)
+{
+    public double TotalMeters =>
+        this switch
+        {
+            Meters m => m.Value,
+            Feet f => f.Value * 0.3048,
+            _ => throw new InvalidOperationException("The Length has no value."),
+        };
+
+    public Length Add(Length other) => new Meters(TotalMeters + other.TotalMeters);
+}
diff --git a/Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ClosedAndUnionModifiers.test b/Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ClosedAndUnionModifiers.test
new file mode 100644
index 000000000..341f3761c
--- /dev/null
+++ b/Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ClosedAndUnionModifiers.test
@@ -0,0 +1,19 @@
+public closed record class JobStatus;
+
+public record class Queued : JobStatus;
+
+public record class Running(int PercentComplete) : JobStatus;
+
+public union Pet(Cat, Dog, Bird);
+
+public union Length(Meters, Feet)
+{
+    public double TotalMeters => this switch
+    {
+        Meters m => m.Value,
+        Feet f => f.Value * 0.3048,
+        _ => throw new InvalidOperationException("The Length has no value."),
+    };
+
+    public Length Add(Length other) => new Meters(TotalMeters + other.TotalMeters);
+}