diff --git a/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet10_0.verified.txt b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet10_0.verified.txt
new file mode 100644
index 0000000000..5585abcba2
--- /dev/null
+++ b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet10_0.verified.txt
@@ -0,0 +1,33 @@
+[  
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+using System;
+using System.Runtime.CompilerServices;
+using TUnit.Assertions.Core;
+using TUnit.Assertions.Enums;
+using TUnit.Assertions.Tests.TestData;
+
+namespace TUnit.Assertions.Extensions;
+
+/// <summary>
+/// Generated extension methods for ConcreteReceiverWithExtraGenericAssertion.
+/// </summary>
+public static partial class ConcreteReceiverWithExtraGenericAssertionExtensions
+{
+
+    /// <summary>
+    /// Extension method for ConcreteReceiverWithExtraGenericAssertion.
+    /// </summary>
+    public static ConcreteReceiverWithExtraGenericAssertion<T> ConcreteReceiverWithExtraGenericMatches<TActual, T>(this IAssertionSource<TActual> source, System.Func<T, bool> predicate, [CallerArgumentExpression(nameof(predicate))] string? predicateExpression = null)
+        where TActual : System.Exception
+    {
+        source.Context.ExpressionBuilder.Append(".ConcreteReceiverWithExtraGenericMatches(");
+        source.Context.ExpressionBuilder.Append(predicateExpression);
+        source.Context.ExpressionBuilder.Append(")");
+        return new ConcreteReceiverWithExtraGenericAssertion<T>(source.Context.Map<System.Exception>(static x => (System.Exception?)x), predicate);
+    }
+}
+
+]
\ No newline at end of file
diff --git a/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet8_0.verified.txt b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet8_0.verified.txt
new file mode 100644
index 0000000000..5585abcba2
--- /dev/null
+++ b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet8_0.verified.txt
@@ -0,0 +1,33 @@
+[  
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+using System;
+using System.Runtime.CompilerServices;
+using TUnit.Assertions.Core;
+using TUnit.Assertions.Enums;
+using TUnit.Assertions.Tests.TestData;
+
+namespace TUnit.Assertions.Extensions;
+
+/// <summary>
+/// Generated extension methods for ConcreteReceiverWithExtraGenericAssertion.
+/// </summary>
+public static partial class ConcreteReceiverWithExtraGenericAssertionExtensions
+{
+
+    /// <summary>
+    /// Extension method for ConcreteReceiverWithExtraGenericAssertion.
+    /// </summary>
+    public static ConcreteReceiverWithExtraGenericAssertion<T> ConcreteReceiverWithExtraGenericMatches<TActual, T>(this IAssertionSource<TActual> source, System.Func<T, bool> predicate, [CallerArgumentExpression(nameof(predicate))] string? predicateExpression = null)
+        where TActual : System.Exception
+    {
+        source.Context.ExpressionBuilder.Append(".ConcreteReceiverWithExtraGenericMatches(");
+        source.Context.ExpressionBuilder.Append(predicateExpression);
+        source.Context.ExpressionBuilder.Append(")");
+        return new ConcreteReceiverWithExtraGenericAssertion<T>(source.Context.Map<System.Exception>(static x => (System.Exception?)x), predicate);
+    }
+}
+
+]
\ No newline at end of file
diff --git a/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet9_0.verified.txt b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet9_0.verified.txt
new file mode 100644
index 0000000000..5585abcba2
--- /dev/null
+++ b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.DotNet9_0.verified.txt
@@ -0,0 +1,33 @@
+[  
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+using System;
+using System.Runtime.CompilerServices;
+using TUnit.Assertions.Core;
+using TUnit.Assertions.Enums;
+using TUnit.Assertions.Tests.TestData;
+
+namespace TUnit.Assertions.Extensions;
+
+/// <summary>
+/// Generated extension methods for ConcreteReceiverWithExtraGenericAssertion.
+/// </summary>
+public static partial class ConcreteReceiverWithExtraGenericAssertionExtensions
+{
+
+    /// <summary>
+    /// Extension method for ConcreteReceiverWithExtraGenericAssertion.
+    /// </summary>
+    public static ConcreteReceiverWithExtraGenericAssertion<T> ConcreteReceiverWithExtraGenericMatches<TActual, T>(this IAssertionSource<TActual> source, System.Func<T, bool> predicate, [CallerArgumentExpression(nameof(predicate))] string? predicateExpression = null)
+        where TActual : System.Exception
+    {
+        source.Context.ExpressionBuilder.Append(".ConcreteReceiverWithExtraGenericMatches(");
+        source.Context.ExpressionBuilder.Append(predicateExpression);
+        source.Context.ExpressionBuilder.Append(")");
+        return new ConcreteReceiverWithExtraGenericAssertion<T>(source.Context.Map<System.Exception>(static x => (System.Exception?)x), predicate);
+    }
+}
+
+]
\ No newline at end of file
diff --git a/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.Net4_7.verified.txt b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.Net4_7.verified.txt
new file mode 100644
index 0000000000..5585abcba2
--- /dev/null
+++ b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.ConcreteReceiverWithExtraGeneric.Net4_7.verified.txt
@@ -0,0 +1,33 @@
+[  
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+
+using System;
+using System.Runtime.CompilerServices;
+using TUnit.Assertions.Core;
+using TUnit.Assertions.Enums;
+using TUnit.Assertions.Tests.TestData;
+
+namespace TUnit.Assertions.Extensions;
+
+/// <summary>
+/// Generated extension methods for ConcreteReceiverWithExtraGenericAssertion.
+/// </summary>
+public static partial class ConcreteReceiverWithExtraGenericAssertionExtensions
+{
+
+    /// <summary>
+    /// Extension method for ConcreteReceiverWithExtraGenericAssertion.
+    /// </summary>
+    public static ConcreteReceiverWithExtraGenericAssertion<T> ConcreteReceiverWithExtraGenericMatches<TActual, T>(this IAssertionSource<TActual> source, System.Func<T, bool> predicate, [CallerArgumentExpression(nameof(predicate))] string? predicateExpression = null)
+        where TActual : System.Exception
+    {
+        source.Context.ExpressionBuilder.Append(".ConcreteReceiverWithExtraGenericMatches(");
+        source.Context.ExpressionBuilder.Append(predicateExpression);
+        source.Context.ExpressionBuilder.Append(")");
+        return new ConcreteReceiverWithExtraGenericAssertion<T>(source.Context.Map<System.Exception>(static x => (System.Exception?)x), predicate);
+    }
+}
+
+]
\ No newline at end of file
diff --git a/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.cs b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.cs
index 95b8029a5e..7ecadf520d 100644
--- a/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.cs
+++ b/TUnit.Assertions.SourceGenerator.Tests/AssertionExtensionGeneratorTests.cs
@@ -1,3 +1,5 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using TUnit.Assertions.SourceGenerator.Generators;
 using TUnit.Assertions.SourceGenerator.Tests.Options;
 
@@ -49,6 +51,58 @@ public Task MultipleGenericParameters() => RunTest(
             await Assert.That(extensionFile!).Contains("<TValue, TTarget>");
         });
 
+    [Test]
+    public Task ConcreteReceiverWithExtraGeneric() => RunTest(
+        Path.Combine(Sourcy.Git.RootDirectory.FullName,
+            "TUnit.Assertions.SourceGenerator.Tests",
+            "TestData",
+            "ConcreteReceiverWithExtraGenericAssertion.cs"),
+        async generatedFiles =>
+        {
+            await Assert.That(generatedFiles).Count().IsEqualTo(1);
+            var extensionFile = generatedFiles.FirstOrDefault(f => f.Contains("ConcreteReceiverWithExtraGenericMatches"));
+            await Assert.That(extensionFile).IsNotNull();
+            await Assert.That(extensionFile!).Contains("ConcreteReceiverWithExtraGenericMatches");
+
+            // The covariant receiver-type parameter (if applied) and the class's own type
+            // parameter must appear in a single merged generic parameter list. Two adjacent
+            // blocks (<TActual><T> or <X><Y>) is invalid C# syntax. The compile-clean check
+            // below is the structural guard; this surface-level assertion pins the absence
+            // of adjacent generic-parameter blocks regardless of whether covariance fired
+            // for this fixture's compilation context.
+            await Assert.That(extensionFile!).DoesNotContain("><");
+
+            // Compile-clean gate: parse + compile the generated source through Roslyn and
+            // assert no error-severity diagnostic. Catches the entire class of emit-syntax
+            // bugs (mis-paired brackets, wrong default rendering, adjacent generic blocks)
+            // regardless of specific diagnostic id.
+            var trees = generatedFiles
+                .Select(source => CSharpSyntaxTree.ParseText(source))
+                .ToArray();
+
+            var compilation = CSharpCompilation.Create(
+                "CompileCheck",
+                trees,
+                ReferencesHelper.References,
+                new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+
+            // On the net472 leg of CI, the Polyfill assembly's CallerArgumentExpressionAttribute
+            // is declared internal, which produces a CS0122 ('inaccessible due to its protection
+            // level') false positive when Roslyn compiles the generator's output through the test
+            // project's reference set. Filter CS0122 only on net472; the emit shape is still
+            // pinned by the `.Net4_7` snapshot file. On modern TFMs the BCL attribute is public,
+            // so CS0122 (if it ever appears) would be a genuine signal and is not filtered.
+            var errors = compilation.GetDiagnostics()
+                .Where(d => d.Severity == DiagnosticSeverity.Error)
+#if NETFRAMEWORK
+                .Where(d => !string.Equals(d.Id, "CS0122", StringComparison.Ordinal))
+#endif
+                .Select(d => $"{d.Id}: {d.GetMessage()}")
+                .ToArray();
+
+            await Assert.That(errors).IsEmpty();
+        });
+
     [Test]
     public Task AssertionWithOptionalParameter() => RunTest(
         Path.Combine(Sourcy.Git.RootDirectory.FullName,
diff --git a/TUnit.Assertions.SourceGenerator.Tests/TestData/ConcreteReceiverWithExtraGenericAssertion.cs b/TUnit.Assertions.SourceGenerator.Tests/TestData/ConcreteReceiverWithExtraGenericAssertion.cs
new file mode 100644
index 0000000000..474737ce20
--- /dev/null
+++ b/TUnit.Assertions.SourceGenerator.Tests/TestData/ConcreteReceiverWithExtraGenericAssertion.cs
@@ -0,0 +1,32 @@
+using TUnit.Assertions.Attributes;
+using TUnit.Assertions.Core;
+
+namespace TUnit.Assertions.Tests.TestData;
+
+/// <summary>Test case: an <see cref="AssertionExtensionAttribute"/>-decorated
+/// <see cref="Assertion{T}"/> subclass over a CONCRETE receiver type that ALSO declares
+/// its own generic type parameter on the class. The generated extension method must merge
+/// both the covariant receiver-type parameter and the class's own type parameter into a
+/// single generic parameter list (e.g. <c>&lt;TActual, T&gt;</c>), NOT emit them as two
+/// adjacent blocks (<c>&lt;TActual&gt;&lt;T&gt;</c>) which is invalid C# syntax.
+/// Uses <see cref="System.Exception"/> as the receiver to anchor the fixture to a BCL
+/// non-sealed class (the covariance candidate the generator looks for) without adding
+/// a stand-in type to the test surface.</summary>
+[AssertionExtension("ConcreteReceiverWithExtraGenericMatches")]
+public class ConcreteReceiverWithExtraGenericAssertion<T> : Assertion<System.Exception>
+{
+    private readonly Func<T, bool> _predicate;
+
+    public ConcreteReceiverWithExtraGenericAssertion(AssertionContext<System.Exception> context, Func<T, bool> predicate)
+        : base(context)
+    {
+        _predicate = predicate;
+    }
+
+    protected override Task<AssertionResult> CheckAsync(EvaluationMetadata<System.Exception> metadata)
+    {
+        return Task.FromResult(AssertionResult.Passed);
+    }
+
+    protected override string GetExpectation() => "to match the predicate";
+}
diff --git a/TUnit.Assertions.SourceGenerator/Generators/AssertionExtensionGenerator.cs b/TUnit.Assertions.SourceGenerator/Generators/AssertionExtensionGenerator.cs
index 929563d84a..a3f3fed290 100644
--- a/TUnit.Assertions.SourceGenerator/Generators/AssertionExtensionGenerator.cs
+++ b/TUnit.Assertions.SourceGenerator/Generators/AssertionExtensionGenerator.cs
@@ -384,11 +384,22 @@ private static void GenerateExtensionMethod(
         }
 
         sourceBuilder.Append($"    public static {returnType} {methodName}");
+
+        // Merge the covariant receiver-type parameter (if any) with the assertion class's own
+        // type parameters into a single generic parameter list. Emitting them as two adjacent
+        // <X><Y> blocks produces invalid C# when both are present (e.g. an Assertion<Concrete>
+        // subclass that also declares its own <T>: the receiver-type covariance adds TActual,
+        // the class adds T, and the method signature must be <TActual, T>, not <TActual><T>).
+        var methodGenericParams = new List<string>();
         if (genericTypeParam != null)
         {
-            sourceBuilder.Append($"<{genericTypeParam}>");
+            methodGenericParams.Add(genericTypeParam);
+        }
+        methodGenericParams.AddRange(genericParams);
+        if (methodGenericParams.Count > 0)
+        {
+            sourceBuilder.Append($"<{string.Join(", ", methodGenericParams)}>");
         }
-        sourceBuilder.Append(genericParamsString);
         sourceBuilder.Append("(");
         sourceBuilder.Append($"this {sourceType} source");