diff --git a/src/BizHawk.Client.Common/Api/Classes/EmulationApi.cs b/src/BizHawk.Client.Common/Api/Classes/EmulationApi.cs
index 59038831bd..0483759ac7 100644
--- a/src/BizHawk.Client.Common/Api/Classes/EmulationApi.cs
+++ b/src/BizHawk.Client.Common/Api/Classes/EmulationApi.cs
@@ -111,7 +111,7 @@ namespace BizHawk.Client.Common
 			return null;
 		}
 
-		public Dictionary<string, ulong> GetRegisters()
+		public IReadOnlyDictionary<string, ulong> GetRegisters()
 		{
 			try
 			{
diff --git a/src/BizHawk.Client.Common/Api/Classes/MovieApi.cs b/src/BizHawk.Client.Common/Api/Classes/MovieApi.cs
index 1e53078941..ce13a0f3b1 100644
--- a/src/BizHawk.Client.Common/Api/Classes/MovieApi.cs
+++ b/src/BizHawk.Client.Common/Api/Classes/MovieApi.cs
@@ -3,7 +3,6 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 
-using BizHawk.Common;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -73,23 +72,16 @@ namespace BizHawk.Client.Common
 			_movieSession.Movie.Save();
 		}
 
-		public Dictionary<string, string> GetHeader()
-		{
-			var table = new Dictionary<string, string>();
-			if (_movieSession.Movie.NotActive())
-			{
-				return table;
-			}
-			foreach (var (k, v) in _movieSession.Movie.HeaderEntries) table[k] = v;
-			return table;
-		}
+		public IReadOnlyDictionary<string, string> GetHeader()
+			=> _movieSession.Movie.NotActive()
+				? new Dictionary<string, string>()
+				: _movieSession.Movie.HeaderEntries.ToDictionary(static kvp => kvp.Key, static kvp => kvp.Value);
 
-		public List<string> GetComments() => _movieSession.Movie.Comments.ToList();
+		public IReadOnlyList<string> GetComments()
+			=> _movieSession.Movie.Comments.ToList();
 
-		public List<string> GetSubtitles() =>
-			_movieSession.Movie.Subtitles
-				.Select(s => s.ToString())
-				.ToList();
+		public IReadOnlyList<string> GetSubtitles()
+			=> _movieSession.Movie.Subtitles.Select(static s => s.ToString()).ToList();
 
 		public string Filename() => _movieSession.Movie.Filename;
 
diff --git a/src/BizHawk.Client.Common/Api/Interfaces/IEmulationApi.cs b/src/BizHawk.Client.Common/Api/Interfaces/IEmulationApi.cs
index 77e7b11e43..437e35eead 100644
--- a/src/BizHawk.Client.Common/Api/Interfaces/IEmulationApi.cs
+++ b/src/BizHawk.Client.Common/Api/Interfaces/IEmulationApi.cs
@@ -13,7 +13,7 @@ namespace BizHawk.Client.Common
 		int FrameCount();
 		object Disassemble(uint pc, string name = "");
 		ulong? GetRegister(string name);
-		Dictionary<string, ulong> GetRegisters();
+		IReadOnlyDictionary<string, ulong> GetRegisters();
 		void SetRegister(string register, int value);
 		long TotalExecutedCycles();
 		string GetSystemId();
diff --git a/src/BizHawk.Client.Common/Api/Interfaces/IMovieApi.cs b/src/BizHawk.Client.Common/Api/Interfaces/IMovieApi.cs
index bed563b7d7..6538bfbd4b 100644
--- a/src/BizHawk.Client.Common/Api/Interfaces/IMovieApi.cs
+++ b/src/BizHawk.Client.Common/Api/Interfaces/IMovieApi.cs
@@ -21,8 +21,8 @@ namespace BizHawk.Client.Common
 		void SetRerecordCounting(bool counting);
 		void Stop();
 		double GetFps();
-		Dictionary<string, string> GetHeader();
-		List<string> GetComments();
-		List<string> GetSubtitles();
+		IReadOnlyDictionary<string, string> GetHeader();
+		IReadOnlyList<string> GetComments();
+		IReadOnlyList<string> GetSubtitles();
 	}
 }
diff --git a/src/BizHawk.Client.Common/lua/NLuaTableHelper.cs b/src/BizHawk.Client.Common/lua/NLuaTableHelper.cs
index d066f5006b..9a6b8ce211 100644
--- a/src/BizHawk.Client.Common/lua/NLuaTableHelper.cs
+++ b/src/BizHawk.Client.Common/lua/NLuaTableHelper.cs
@@ -36,7 +36,7 @@ namespace BizHawk.Client.Common
 
 		public IEnumerable<T> EnumerateValues<T>(LuaTable table) => table.Values.Cast<T>();
 
-		public LuaTable ListToTable<T>(IList<T> list, int indexFrom = 1)
+		public LuaTable ListToTable<T>(IReadOnlyList<T> list, int indexFrom = 1)
 		{
 			var table = _lua.NewTable();
 			for (int i = 0, l = list.Count; i != l; i++) table[indexFrom + i] = list[i];