diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MapperPropAttribute.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MapperPropAttribute.cs
new file mode 100644
index 0000000000..adc449d0d2
--- /dev/null
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MapperPropAttribute.cs
@@ -0,0 +1,71 @@
+using System;
+using System.IO;
+using System.Linq;
+
+namespace BizHawk.Emulation.Cores.Nintendo.NES
+{
+	[AttributeUsage(AttributeTargets.Field)]
+	public sealed class MapperPropAttribute : Attribute
+	{
+		public string Name { get; }
+
+		public MapperPropAttribute(string name)
+		{
+			Name = name;
+		}
+
+		public MapperPropAttribute()
+		{
+			Name = null;
+		}
+	}
+
+	internal static class AutoMapperProps
+	{
+		public static void Populate(INesBoard board, NES.NESSyncSettings settings)
+		{
+			var fields = board.GetType().GetFields();
+			foreach (var field in fields)
+			{
+				var attrib = field.GetCustomAttributes(typeof(MapperPropAttribute), false).OfType<MapperPropAttribute>().SingleOrDefault();
+				if (attrib == null)
+					continue;
+				string name = attrib.Name ?? field.Name;
+				if (!settings.BoardProperties.ContainsKey(name))
+				{
+					settings.BoardProperties.Add(name, (string)Convert.ChangeType(field.GetValue(board), typeof(string)));
+				}
+			}
+		}
+
+		public static void Apply(INesBoard board)
+		{
+			var fields = board.GetType().GetFields();
+			foreach (var field in fields)
+			{
+				var attribs = field.GetCustomAttributes(false);
+				foreach (var attrib in attribs)
+				{
+					if (attrib is MapperPropAttribute mapperProp)
+					{
+						string name = mapperProp.Name ?? field.Name;
+
+						if (board.InitialRegisterValues.TryGetValue(name, out var Value))
+						{
+							try
+							{
+								field.SetValue(board, Convert.ChangeType(Value, field.FieldType));
+							}
+							catch (Exception e) when (e is InvalidCastException || e is FormatException || e is OverflowException)
+							{
+								throw new InvalidDataException("Auto Mapper Properties were in a bad format!", e);
+							}
+						}
+
+						break;
+					}
+				}
+			}
+		}
+	}
+}
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/NES.BoardSystem.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/NES.BoardSystem.cs
index 686eae728d..f1f1c56e7a 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/NES.BoardSystem.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/NES.BoardSystem.cs
@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
 using System.Xml;
 using BizHawk.Common;
 using BizHawk.Emulation.Common;
@@ -398,68 +397,4 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 			}
 		}
 	}
-
-	[AttributeUsage(AttributeTargets.Field)]
-	public sealed class MapperPropAttribute : Attribute
-	{
-		public string Name { get; }
-
-		public MapperPropAttribute(string name)
-		{
-			Name = name;
-		}
-
-		public MapperPropAttribute()
-		{
-			Name = null;
-		}
-	}
-
-	internal static class AutoMapperProps
-	{
-		public static void Populate(INesBoard board, NES.NESSyncSettings settings)
-		{
-			var fields = board.GetType().GetFields();
-			foreach (var field in fields)
-			{
-				var attrib = field.GetCustomAttributes(typeof(MapperPropAttribute), false).OfType<MapperPropAttribute>().SingleOrDefault();
-				if (attrib == null)
-					continue;
-				string Name = attrib.Name ?? field.Name;
-				if (!settings.BoardProperties.ContainsKey(Name))
-				{
-					settings.BoardProperties.Add(Name, (string)Convert.ChangeType(field.GetValue(board), typeof(string)));
-				}
-			}
-		}
-
-		public static void Apply(INesBoard board)
-		{
-			var fields = board.GetType().GetFields();
-			foreach (var field in fields)
-			{
-				var attribs = field.GetCustomAttributes(false);
-				foreach (var attrib in attribs)
-				{
-					if (attrib is MapperPropAttribute)
-					{
-						string Name = ((MapperPropAttribute)attrib).Name ?? field.Name;
-
-						if (board.InitialRegisterValues.TryGetValue(Name, out var Value))
-						{
-							try
-							{
-								field.SetValue(board, Convert.ChangeType(Value, field.FieldType));
-							}
-							catch (Exception e) when (e is InvalidCastException || e is FormatException || e is OverflowException)
-							{
-								throw new InvalidDataException("Auto Mapper Properties were in a bad format!", e);
-							}
-						}
-						break;
-					}
-				}
-			}
-		}
-	}
 }