diff --git a/src/BizHawk.Common/CustomCollections.cs b/src/BizHawk.Common/CustomCollections.cs
index 8f0eec5c63..2df9d75dfd 100644
--- a/src/BizHawk.Common/CustomCollections.cs
+++ b/src/BizHawk.Common/CustomCollections.cs
@@ -4,17 +4,28 @@ using System.Linq;
 
 namespace BizHawk.Common
 {
-	public class SortedList<T> : IList<T>
+	public class SortedList<T> : IList, IList<T>, IReadOnlyList<T>
 		where T : IComparable<T>
 	{
 		private const string ERR_MSG_OUT_OF_ORDER = "setting/inserting elements must preserve ordering";
 
+		private const string ERR_MSG_WRONG_TYPE = "wrong type";
+
 		protected readonly List<T> _list;
 
 		public virtual int Count => _list.Count;
 
+		bool IList.IsFixedSize
+			=> false;
+
 		public virtual bool IsReadOnly { get; } = false;
 
+		bool ICollection.IsSynchronized
+			=> false;
+
+		object ICollection.SyncRoot
+			=> this;
+
 		protected SortedList(List<T> wrapped)
 			=> _list = wrapped;
 
@@ -46,20 +57,43 @@ namespace BizHawk.Common
 			}
 		}
 
+		object? IList.this[int index]
+		{
+			get => _list[index];
+			set
+			{
+				if (value is not T value1) throw new ArgumentException(paramName: nameof(value), message: ERR_MSG_WRONG_TYPE);
+				this[index] = value1;
+			}
+		}
+
 		public virtual void Add(T item)
 		{
 			var i = _list.BinarySearch(item);
 			_list.Insert(i < 0 ? ~i : i, item);
 		}
 
+		int IList.Add(object? item)
+		{
+			if (item is not T item1) throw new ArgumentException(paramName: nameof(item), message: ERR_MSG_WRONG_TYPE);
+			Add(item1);
+			return IndexOf(item1);
+		}
+
 		public virtual int BinarySearch(T item) => _list.BinarySearch(item);
 
 		public virtual void Clear() => _list.Clear();
 
 		public virtual bool Contains(T item) => !(_list.BinarySearch(item) < 0); // can't use `!= -1`, BinarySearch can return multiple negative values
 
+		bool IList.Contains(object? item)
+			=> item is T item1 && Contains(item1);
+
 		public virtual void CopyTo(T[] array, int arrayIndex) => _list.CopyTo(array, arrayIndex);
 
+		void ICollection.CopyTo(Array array, int arrayIndex)
+			=> ((ICollection) _list).CopyTo(array, arrayIndex);
+
 		public T FirstOrDefault()
 			=> _list.Count is 0 ? default! : _list[0];
 
@@ -79,6 +113,11 @@ namespace BizHawk.Common
 			return i < 0 ? -1 : i;
 		}
 
+		int IList.IndexOf(object? item)
+			=> item is T item1
+				? IndexOf(item1)
+				: throw new ArgumentException(paramName: nameof(item), message: ERR_MSG_WRONG_TYPE);
+
 		public virtual void Insert(int index, T item)
 		{
 			// allowing appends per `IList<T>` docs
@@ -94,6 +133,12 @@ namespace BizHawk.Common
 			else throw new NotSupportedException(ERR_MSG_OUT_OF_ORDER);
 		}
 
+		void IList.Insert(int index, object? item)
+		{
+			if (item is not T item1) throw new ArgumentException(paramName: nameof(item), message: ERR_MSG_WRONG_TYPE);
+			Insert(index, item1);
+		}
+
 		public T LastOrDefault()
 			=> _list.Count is 0 ? default! : _list[_list.Count - 1];
 
@@ -109,6 +154,12 @@ namespace BizHawk.Common
 #endif
 		}
 
+		void IList.Remove(object? item)
+		{
+			if (item is not T item1) throw new ArgumentException(paramName: nameof(item), message: ERR_MSG_WRONG_TYPE);
+			_ = Remove(item1);
+		}
+
 
 		public virtual int RemoveAll(Predicate<T> match) => _list.RemoveAll(match);