diff --git a/src/Riok.Mapperly/AnalyzerReleases.Shipped.md b/src/Riok.Mapperly/AnalyzerReleases.Shipped.md
index a3902060f4..8c66ba596a 100644
--- a/src/Riok.Mapperly/AnalyzerReleases.Shipped.md
+++ b/src/Riok.Mapperly/AnalyzerReleases.Shipped.md
@@ -102,3 +102,4 @@ RMG040  | Mapper   | Error    | A target enum member value does not match the ta
 RMG041  | Mapper   | Error    | A source enum member value does not match the source enum type
 RMG042  | Mapper   | Error    | The type of the enum fallback value does not match the target enum type
 RMG043  | Mapper   | Warning  | Enum fallback values are only supported for the ByName and ByValueCheckDefined strategies, but not for the ByValue strategy
+RMG044  | Mapper   | Error    | This C# language version is not supported by Mapperly
diff --git a/src/Riok.Mapperly/Diagnostics/DiagnosticDescriptors.cs b/src/Riok.Mapperly/Diagnostics/DiagnosticDescriptors.cs
index 7f9f21a9a5..3c0f484b34 100644
--- a/src/Riok.Mapperly/Diagnostics/DiagnosticDescriptors.cs
+++ b/src/Riok.Mapperly/Diagnostics/DiagnosticDescriptors.cs
@@ -383,4 +383,13 @@ internal static class DiagnosticDescriptors
         DiagnosticSeverity.Warning,
         true
     );
+
+    public static readonly DiagnosticDescriptor LanguageVersionNotSupported = new DiagnosticDescriptor(
+        "RMG044",
+        "This C# language version is not supported by Mapperly",
+        "Mapperly does not support the C# language version {0} but requires at C# least version {1}",
+        DiagnosticCategories.Mapper,
+        DiagnosticSeverity.Error,
+        true
+    );
 }
diff --git a/src/Riok.Mapperly/MapperGenerator.cs b/src/Riok.Mapperly/MapperGenerator.cs
index 71ccc4e7a7..1ee195ea45 100644
--- a/src/Riok.Mapperly/MapperGenerator.cs
+++ b/src/Riok.Mapperly/MapperGenerator.cs
@@ -1,10 +1,12 @@
 using System.Collections.Immutable;
 using System.Text;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Text;
 using Riok.Mapperly.Abstractions;
 using Riok.Mapperly.Descriptors;
+using Riok.Mapperly.Diagnostics;
 using Riok.Mapperly.Emit;
 using Riok.Mapperly.Helpers;
 
@@ -23,6 +25,8 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
     {
         var mapperClassDeclarations = SyntaxProvider.GetClassDeclarations(context);
 
+        context.ReportDiagnostics(context.CompilationProvider.Select(static (compilation, ct) => BuildCompilationDiagnostics(compilation)));
+
         var compilationAndMappers = context.CompilationProvider.Combine(mapperClassDeclarations.Collect());
         var mappersWithDiagnostics = compilationAndMappers.Select(
             static (x, cancellationToken) => BuildDescriptors(x.Left, x.Right, cancellationToken)
@@ -89,4 +93,20 @@ CancellationToken cancellationToken
         cancellationToken.ThrowIfCancellationRequested();
         return new MapperResults(members.ToImmutableEquatableArray(), diagnostics.ToImmutableEquatableArray());
     }
+
+    private static ImmutableEquatableArray<Diagnostic> BuildCompilationDiagnostics(Compilation compilation)
+    {
+        if (compilation is CSharpCompilation { LanguageVersion: < LanguageVersion.CSharp9 } cSharpCompilation)
+        {
+            var diagnostic = Diagnostic.Create(
+                DiagnosticDescriptors.LanguageVersionNotSupported,
+                null,
+                cSharpCompilation.LanguageVersion.ToDisplayString(),
+                LanguageVersion.CSharp9.ToDisplayString()
+            );
+            return ImmutableEquatableArray.Create(diagnostic);
+        }
+
+        return ImmutableEquatableArray.Empty<Diagnostic>();
+    }
 }
diff --git a/test/Riok.Mapperly.Tests/Generator/IncrementalGeneratorTest.cs b/test/Riok.Mapperly.Tests/Generator/IncrementalGeneratorTest.cs
index 9da967a7e5..f65afe98cc 100644
--- a/test/Riok.Mapperly.Tests/Generator/IncrementalGeneratorTest.cs
+++ b/test/Riok.Mapperly.Tests/Generator/IncrementalGeneratorTest.cs
@@ -35,17 +35,17 @@ public void AddingNewMapperDoesNotRegenerateOriginal()
 
         var secondary = TestSourceBuilder.SyntaxTree(
             """
-                    using Riok.Mapperly.Abstractions;
+                  using Riok.Mapperly.Abstractions;
 
-                    namespace Test.B
+                  namespace Test.B
+                  {
+                    [Mapper]
+                    internal partial class BarFooMapper
                     {
-                        [Mapper]
-                        internal partial class BarFooMapper
-                        {
-                            internal partial string BarToFoo(string value);
-                        }
+                        internal partial string BarToFoo(string value);
                     }
-                    """
+                  }
+                  """
         );
 
         var syntaxTree = CSharpSyntaxTree.ParseText(source, CSharpParseOptions.Default);
diff --git a/test/Riok.Mapperly.Tests/Mapping/MapperTest.cs b/test/Riok.Mapperly.Tests/Mapping/MapperTest.cs
index 9cc6e621a5..339931fcae 100644
--- a/test/Riok.Mapperly.Tests/Mapping/MapperTest.cs
+++ b/test/Riok.Mapperly.Tests/Mapping/MapperTest.cs
@@ -1,3 +1,6 @@
+using Microsoft.CodeAnalysis.CSharp;
+using Riok.Mapperly.Diagnostics;
+
 namespace Riok.Mapperly.Tests.Mapping;
 
 [UsesVerify]
@@ -108,4 +111,18 @@ public partial class CarMapper
 
         return TestHelper.VerifyGenerator(source);
     }
+
+    [Fact]
+    public void LanguageLevelLower9ShouldDiagnostic()
+    {
+        var source = TestSourceBuilder.Mapping("string", "int");
+        TestHelper
+            .GenerateMapper(source, TestHelperOptions.AllowDiagnostics with { LanguageVersion = LanguageVersion.CSharp8 })
+            .Should()
+            .HaveDiagnostic(
+                DiagnosticDescriptors.LanguageVersionNotSupported,
+                "Mapperly does not support the C# language version 8.0 but requires at C# least version 9.0"
+            )
+            .HaveAssertedAllDiagnostics();
+    }
 }