Class types with layout that inherit from System.Object should be ManagedSequential

src/coreclr/vm/classlayoutinfo.cpp

@@ -628,7 +628,7 @@ VOID EEClassLayoutInfo::CollectLayoutFieldMetadataThrowing(
     // Check if this type might be ManagedSequential. Only valuetypes marked Sequential can be
     // ManagedSequential. Other issues checked below might also disqualify the type.
     if ( (!fExplicitOffsets) &&    // Is it marked sequential?
-         (pParentMT && (pParentMT->IsValueTypeClass() || pParentMT->IsManagedSequential()))  // Is it a valuetype or derived from a qualifying valuetype?
+         (pParentMT && (pParentMT->IsObjectClass() || pParentMT->IsValueTypeClass() || pParentMT->IsManagedSequential()))  // Is it a valuetype or derived from a qualifying valuetype?
        )
     {
         fDisqualifyFromManagedSequential = FALSE;

src/tests/Loader/classloader/SequentialLayout/ManagedSequential/ManagedSequential.cs

@@ -0,0 +1,68 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using Xunit;
+
+[SkipOnMono("This test suite tests CoreCLR and Crossgen2/NativeAOT-specific layout rules.")]
+unsafe class ManagedSequential
+{
+    [StructLayout(LayoutKind.Sequential)]
+    class LayoutClassObjectBase
+    {
+        public byte b1;
+        public long l1;
+    }
+    class AutoClassLayoutBase : LayoutClassObjectBase
+    {
+        public byte b2;
+        public long l2;
+    }
+
+    class AutoClassObjectBase
+    {
+        public byte b1;
+        public long l1;
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    class LayoutClassLayoutBase : LayoutClassObjectBase
+    {
+        public byte b2;
+        public long l2;
+    }
+
+    [Fact]
+    public static void LayoutClassObjectBaseIsManagedSequential()
+    {
+        var o = new LayoutClassObjectBase();
+        // Validate that the long member is placed after the byte member, as is done with sequential layout in this case.
+        Assert.Equal(8, (int)Unsafe.ByteOffset(ref o.b1, ref Unsafe.As<long, byte>(ref o.l1)));
+    }
+
+    [Fact]
+    public static void LayoutClassLayoutBaseIsManagedSequential()
+    {
+        var o = new LayoutClassLayoutBase();
+        // Validate that the long member is placed after the byte member, as is done with sequential layout in this case.
+        Assert.Equal(8, (int)Unsafe.ByteOffset(ref o.b2, ref Unsafe.As<long, byte>(ref o.l2)));
+    }
+
+    [Fact]
+    public static void AutoClassLayoutBaseIsManagedSequential()
+    {
+        var o = new AutoClassLayoutBase();
+        // Validate that the long member is placed before the byte member, as is done with auto layout in this case.
+        Assert.Equal(-8, (int)Unsafe.ByteOffset(ref o.b2, ref Unsafe.As<long, byte>(ref o.l2)));
+    }
+
+    [Fact]
+    public static void AutoClassObjectBaseIsManagedSequential()
+    {
+        var o = new AutoClassObjectBase();
+        // Validate that the long member is placed before the byte member, as is done with auto layout in this case.
+        Assert.Equal(-8, (int)Unsafe.ByteOffset(ref o.b1, ref Unsafe.As<long, byte>(ref o.l1)));
+    }
+}

src/tests/Loader/classloader/SequentialLayout/ManagedSequential/ManagedSequential.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>