diff --git a/Parser/Internal/SyntaxFactory.Generated.cs b/Parser/Internal/SyntaxFactory.Generated.cs
index 6652d9a..833aaf2 100644
--- a/Parser/Internal/SyntaxFactory.Generated.cs
+++ b/Parser/Internal/SyntaxFactory.Generated.cs
@@ -1,3 +1,4 @@
+#nullable enable
 namespace Parser.Internal
 {
     internal partial class SyntaxFactory
diff --git a/Parser/Internal/SyntaxNode.Generated.cs b/Parser/Internal/SyntaxNode.Generated.cs
index 54d5211..594154d 100644
--- a/Parser/Internal/SyntaxNode.Generated.cs
+++ b/Parser/Internal/SyntaxNode.Generated.cs
@@ -1,3 +1,4 @@
+#nullable enable
 namespace Parser.Internal
 {
     internal class FileSyntaxNode : SyntaxNode
diff --git a/Parser/SyntaxNode.Generated.cs b/Parser/SyntaxNode.Generated.cs
index bb59e96..d3f5bec 100644
--- a/Parser/SyntaxNode.Generated.cs
+++ b/Parser/SyntaxNode.Generated.cs
@@ -1,3 +1,4 @@
+#nullable enable
 namespace Parser
 {
     public class FileSyntaxNode : SyntaxNode
diff --git a/Parser/SyntaxVisitor.Generated.cs b/Parser/SyntaxVisitor.Generated.cs
index c76edaa..c3f5585 100644
--- a/Parser/SyntaxVisitor.Generated.cs
+++ b/Parser/SyntaxVisitor.Generated.cs
@@ -1,3 +1,4 @@
+#nullable enable
 namespace Parser
 {
     public partial class SyntaxVisitor
diff --git a/SyntaxGenerator/GenerateSyntax.cs b/SyntaxGenerator/GenerateSyntax.cs
index da536f2..24fb42a 100644
--- a/SyntaxGenerator/GenerateSyntax.cs
+++ b/SyntaxGenerator/GenerateSyntax.cs
@@ -305,7 +305,7 @@ namespace SyntaxGenerator
 
         private static string GenerateInternalSyntaxNodeFile(SyntaxDescription syntax)
         {
-            var header = $"namespace {InternalNamespace}\n";
+            var header = $"#nullable enable\nnamespace {InternalNamespace}\n";
             var classes = string.Join(
                 "\n",
                 syntax.Nodes.Select(GenerateInternalClass)
@@ -315,7 +315,7 @@ namespace SyntaxGenerator
 
         private static string GenerateSyntaxNodeFile(SyntaxDescription syntax)
         {
-            var header = $"namespace {OuterNamespace}\n";
+            var header = $"#nullable enable\nnamespace {OuterNamespace}\n";
             var classes = string.Join(
                 "\n",
                 syntax.Nodes.Select(GenerateClass)
@@ -358,7 +358,7 @@ namespace SyntaxGenerator
 
         private static string GenerateSyntaxFactoryFile(SyntaxDescription syntax)
         {
-            var header = $"namespace {InternalNamespace}\n{{\n    internal partial class SyntaxFactory\n";
+            var header = $"#nullable enable\nnamespace {InternalNamespace}\n{{\n    internal partial class SyntaxFactory\n";
             var methods = string.Join(
                 "\n",
                 syntax.Nodes.Select(GenerateFactoryMethod)
@@ -375,7 +375,7 @@ namespace SyntaxGenerator
 
         private static string GenerateSyntaxVisitorFile(SyntaxDescription syntax)
         {
-            var header = $"namespace {OuterNamespace}\n{{\n    public partial class SyntaxVisitor\n";
+            var header = $"#nullable enable\nnamespace {OuterNamespace}\n{{\n    public partial class SyntaxVisitor\n";
             var methods = string.Join(
                 "\n",
                Visitors.Select(GenerateVisitor));