diff --git a/AACS/CopyrightRecord.cs b/AACS/CopyrightRecord.cs
index 221a4d8..7a223d5 100644
--- a/AACS/CopyrightRecord.cs
+++ b/AACS/CopyrightRecord.cs
@@ -1,13 +1,17 @@
+using System.Runtime.InteropServices;
+
 namespace SabreTools.Models.AACS
 {
     /// <summary>
     /// This record type is undocumented but found in real media key blocks
     /// </summary>
+    [StructLayout(LayoutKind.Sequential)]
     public sealed class CopyrightRecord : Record
     {
         /// <summary>
         /// Null-terminated ASCII string representing the copyright
         /// </summary>
-        public string? Copyright { get; set; }
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string? Copyright;
     }
 }
\ No newline at end of file
diff --git a/PortableExecutable/MenuItemExtended.cs b/PortableExecutable/MenuItemExtended.cs
index 771fedc..4b4a36c 100644
--- a/PortableExecutable/MenuItemExtended.cs
+++ b/PortableExecutable/MenuItemExtended.cs
@@ -1,37 +1,44 @@
-namespace SabreTools.Models.PortableExecutable
+using System.Runtime.InteropServices;
+
+namespace SabreTools.Models.PortableExecutable
 {
     /// <summary>
     /// Defines a menu item in an extended menu template. This structure definition is for
     /// explanation only; it is not present in any standard header file.
     /// </summary>
     /// <see href="https://learn.microsoft.com/en-us/windows/win32/menurc/menuex-template-item"/>
+    [StructLayout(LayoutKind.Sequential)]
     public sealed class MenuItemExtended
     {
         /// <summary>
         /// Describes the menu item.
         /// </summary>
-        public MenuFlags ItemType { get; set; }
+        [MarshalAs(UnmanagedType.U4)]
+        public MenuFlags ItemType;
 
         /// <summary>
         /// Describes the menu item.
         /// </summary>
-        public MenuFlags State { get; set; }
+        [MarshalAs(UnmanagedType.U4)]
+        public MenuFlags State;
 
         /// <summary>
         /// A numeric expression that identifies the menu item that is passed in the
         /// WM_COMMAND message.
         /// </summary>
-        public uint ID { get; set; }
+        public uint ID;
 
         /// <summary>
         /// A set of bit flags that specify the type of menu item.
         /// </summary>
-        public MenuFlags Flags { get; set; }
+        [MarshalAs(UnmanagedType.U4)]
+        public MenuFlags Flags;
 
         /// <summary>
         /// A null-terminated Unicode string that contains the text for this menu item.
         /// There is no fixed limit on the size of this string.
         /// </summary>
-        public string? MenuText { get; set; }
+        [MarshalAs(UnmanagedType.LPWStr)]
+        public string? MenuText;
     }
 }
diff --git a/PortableExecutable/NB10ProgramDatabase.cs b/PortableExecutable/NB10ProgramDatabase.cs
index 591ad33..70ac2ea 100644
--- a/PortableExecutable/NB10ProgramDatabase.cs
+++ b/PortableExecutable/NB10ProgramDatabase.cs
@@ -1,39 +1,43 @@
-namespace SabreTools.Models.PortableExecutable
+using System.Runtime.InteropServices;
+
+namespace SabreTools.Models.PortableExecutable
 {
     /// <summary>
     /// PDB 2.0 files
     /// </summary>
     /// <see href="https://www.debuginfo.com/articles/debuginfomatch.html"/>
+    [StructLayout(LayoutKind.Sequential)]
     public sealed class NB10ProgramDatabase
     {
         /// <summary>
         /// "CodeView signature, equal to “NB10” 
         /// </summary>
-        public uint Signature { get; set; }
+        public uint Signature;
 
         /// <summary>
         /// CodeView offset. Set to 0, because debug information
         /// is stored in a separate file.
         /// </summary>
-        public uint Offset { get; set; }
+        public uint Offset;
 
         /// <summary>
         /// The time when debug information was created (in seconds
         /// since 01.01.1970) 
         /// </summary>
-        public uint Timestamp { get; set; }
+        public uint Timestamp;
 
         /// <summary>
         /// Ever-incrementing value, which is initially set to 1 and
         /// incremented every time when a part of the PDB file is updated
         /// without rewriting the whole file. 
         /// </summary>
-        public uint Age { get; set; }
+        public uint Age;
 
         /// <summary>
         /// Null-terminated name of the PDB file. It can also contain full
         /// or partial path to the file. 
         /// </summary>
-        public string? PdbFileName { get; set; }
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string? PdbFileName;
     }
 }