diff --git a/src/BizHawk.Client.Common/RomGame.cs b/src/BizHawk.Client.Common/RomGame.cs
index ee94c2a899..a96cfa9f9f 100644
--- a/src/BizHawk.Client.Common/RomGame.cs
+++ b/src/BizHawk.Client.Common/RomGame.cs
@@ -29,7 +29,7 @@ namespace BizHawk.Client.Common
 				throw new Exception("The file needs to exist, yo.");
 			}
 
-			Extension = file.Extension;
+			Extension = file.Extension.ToUpperInvariant();
 
 			var stream = file.GetStream();
 			int fileLength = (int)stream.Length;
@@ -63,8 +63,8 @@ namespace BizHawk.Client.Common
 			{
 				RomData = FileData;
 			}
-			else if (file.Extension == ".DSK" || file.Extension == ".TAP" || file.Extension == ".TZX" || 
-				file.Extension == ".PZX" || file.Extension == ".CSW" || file.Extension == ".WAV" || file.Extension == ".CDT")
+			else if (file.Extension == ".dsk" || file.Extension == ".tap" || file.Extension == ".tzx" ||
+				file.Extension == ".pzx" || file.Extension == ".csw" || file.Extension == ".wav" || file.Extension == ".cdt")
 			{
 				// these are not roms. unfortunately if treated as such there are certain edge-cases
 				// where a header offset is detected. This should mitigate this issue until a cleaner solution is found 
@@ -79,12 +79,12 @@ namespace BizHawk.Client.Common
 				Buffer.BlockCopy(FileData, headerOffset, RomData, 0, romLength);
 			}
 
-			if (file.Extension == ".SMD")
+			if (file.Extension == ".smd")
 			{
 				RomData = DeInterleaveSMD(RomData);
 			}
 
-			if (file.Extension == ".Z64" || file.Extension == ".N64" || file.Extension == ".V64")
+			if (file.Extension == ".z64" || file.Extension == ".n64" || file.Extension == ".v64")
 			{
 				RomData = MutateSwapN64(RomData);
 			}
@@ -92,7 +92,7 @@ namespace BizHawk.Client.Common
 			// note: this will be taking several hashes, of a potentially large amount of data.. yikes!
 			GameInfo = Database.GetGameInfo(RomData, file.Name);
 
-			if (GameInfo.NotInDatabase && headerOffset == 128 && file.Extension == ".A78")
+			if (GameInfo.NotInDatabase && headerOffset == 128 && file.Extension == ".a78")
 			{
 				// if the game is not in the DB, add the header back in so the core can use it
 				// for now only .A78 games, but probably should be for other systems as well
@@ -104,7 +104,7 @@ namespace BizHawk.Client.Common
 			if (patch != null)
 			{
 				using var patchFile = new HawkFile(patch);
-				patchFile.BindFirstOf("IPS");
+				patchFile.BindFirstOf(".ips");
 				if (patchFile.IsBound)
 				{
 					RomData = IPS.Patch(RomData, patchFile.GetStream());
diff --git a/src/BizHawk.Client.Common/RomLoader.cs b/src/BizHawk.Client.Common/RomLoader.cs
index 7ea52b0857..7c9dde5edb 100644
--- a/src/BizHawk.Client.Common/RomLoader.cs
+++ b/src/BizHawk.Client.Common/RomLoader.cs
@@ -208,9 +208,9 @@ namespace BizHawk.Client.Common
 		{
 			var romExtensions = new[]
 			{
-				"SMS", "SMC", "SFC", "PCE", "SGX", "GG", "SG", "BIN", "GEN", "MD", "SMD", "GB",
-				"NES", "FDS", "ROM", "INT", "GBC", "UNF", "A78", "CRT", "COL", "XML", "Z64",
-				"V64", "N64", "WS", "WSC", "GBA", "32X", "VEC", "O2"
+				".sms", ".smc", ".sfc", ".pce", ".sgx", ".gg", ".sg", ".bin", ".gen", ".md", ".smd", ".gb",
+				".nes", ".fds", ".rom", ".int", ".gbc", ".unf", ".a78", ".crt", ".col", ".xml", ".z64",
+				".v64", ".n64", ".ws", ".wsc", ".gba", ".32x", ".vec", ".o2"
 			};
 
 			// try binding normal rom extensions first
@@ -426,11 +426,11 @@ namespace BizHawk.Client.Common
 			rom = new RomGame(file);
 
 			// hacky for now
-			if (file.Extension.ToLowerInvariant() == ".exe")
+			if (file.Extension == ".exe")
 			{
 				rom.GameInfo.System = "PSX";
 			}
-			else if (file.Extension.ToLowerInvariant() == ".nsf")
+			else if (file.Extension == ".nsf")
 			{
 				rom.GameInfo.System = "NES";
 			}
@@ -685,7 +685,7 @@ namespace BizHawk.Client.Common
 					}
 
 					// not libretro: do extension checking
-					var ext = file.Extension.ToLowerInvariant();
+					var ext = file.Extension;
 					switch (ext)
 					{
 						case ".m3u":
diff --git a/src/BizHawk.Client.EmuHawk/AVOut/FFmpegDownloaderForm.cs b/src/BizHawk.Client.EmuHawk/AVOut/FFmpegDownloaderForm.cs
index 773e6424f5..7b26e38c9a 100644
--- a/src/BizHawk.Client.EmuHawk/AVOut/FFmpegDownloaderForm.cs
+++ b/src/BizHawk.Client.EmuHawk/AVOut/FFmpegDownloaderForm.cs
@@ -81,7 +81,7 @@ namespace BizHawk.Client.EmuHawk
 				//try acquiring file
 				using (var hf = new HawkFile(fn))
 				{
-					using (var exe = hf.BindFirstOf("EXE"))
+					using (var exe = hf.BindFirstOf(".exe"))
 					{
 						var data = exe.ReadAllBytes();
 
diff --git a/src/BizHawk.Common/HawkFile/HawkFile.cs b/src/BizHawk.Common/HawkFile/HawkFile.cs
index 2af5e4f417..3736b32ebb 100644
--- a/src/BizHawk.Common/HawkFile/HawkFile.cs
+++ b/src/BizHawk.Common/HawkFile/HawkFile.cs
@@ -4,8 +4,6 @@ using System.Diagnostics;
 using System.IO;
 using System.Linq;
 
-using BizHawk.Common.StringExtensions;
-
 namespace BizHawk.Common
 {
 	/// <summary>
@@ -54,8 +52,8 @@ namespace BizHawk.Common
 		/// <value>true if a file is bound and the bound file exists</value>
 		public readonly bool Exists;
 
-		/// <summary>returns the extension of Name in uppercase</summary>
-		public string Extension => Path.GetExtension(Name).ToUpperInvariant();
+		/// <value>the file extension (of <see cref="Name"/>); including the leading period and in lowercase</value>
+		public string Extension => Path.GetExtension(Name).ToLowerInvariant();
 
 		/// <value>returns the complete full path of the bound file, excluding the archive member portion</value>
 		public readonly string FullPathWithoutMember;
@@ -175,20 +173,18 @@ namespace BizHawk.Common
 			return ai == null ? null : BindArchiveMember(ai.Value);
 		}
 
+		/// <param name="extensions">File extensions; include the leading period in each, and use lowercase.</param>
 		/// <exception cref="InvalidOperationException">stream already bound</exception>
-		private HawkFile BindByExtensionCore(bool first, params string[] extensions)
+		private HawkFile BindByExtensionCore(string[] extensions, bool onlyBindSingle = false)
 		{
 			if (!_rootExists) return this;
 			if (_boundStream != null) throw new InvalidOperationException("stream already bound!");
-			
-			if(extensions.Any(e=>e.StartsWith(".")))
-				throw new InvalidOperationException("for this purpose extension should not start with a dot");
 
 			if (_archiveItems == null || _extractor == null)
 			{
 				// open uncompressed file
 				if (extensions.Length == 0
-					|| Path.GetExtension(FullPathWithoutMember).Substring(1).In(extensions))
+					|| extensions.Contains(Path.GetExtension(FullPathWithoutMember).ToLowerInvariant()))
 				{
 					BindRoot();
 				}
@@ -197,10 +193,10 @@ namespace BizHawk.Common
 			{
 				if (extensions.Length != 0)
 				{
-					var candidates = _archiveItems.Where(item => Path.GetExtension(item.Name).Substring(1).In(extensions)).ToList();
-					if (candidates.Count != 0 && first || candidates.Count == 1) BindArchiveMember(candidates[0].Index);
+					var candidates = _archiveItems.Where(item => extensions.Contains(Path.GetExtension(item.Name).ToLowerInvariant())).ToList();
+					if (onlyBindSingle ? candidates.Count == 1 : candidates.Count != 0) BindArchiveMember(candidates[0].Index);
 				}
-				else if (first || _archiveItems.Count == 1)
+				else if (!onlyBindSingle || _archiveItems.Count == 1)
 				{
 					BindArchiveMember(0);
 				}
@@ -209,12 +205,24 @@ namespace BizHawk.Common
 			return this;
 		}
 
-		/// <summary>Binds the first item in the archive (or the file itself), assuming that there is anything in the archive.</summary>
-		public HawkFile BindFirst() => BindFirstOf();
+		/// <summary>Binds the first archive member if one exists, or for non-archives, binds the file.</summary>
+		public HawkFile BindFirst() => BindByExtensionCore(Array.Empty<string>());
 
-		/// <summary>Binds the first item in the archive (or the file itself) if the extension matches one of the supplied templates.</summary>
+		/// <summary>
+		/// Binds the first archive member whose file extension is in <paramref name="extensions"/> if one exists,
+		/// or for non-archives, binds the file if its file extension is in <paramref name="extensions"/>.
+		/// </summary>
+		/// <param name="extensions">File extensions; include the leading period in each, and use lowercase.</param>
 		/// <remarks>You probably should use <see cref="BindSoleItemOf"/> or the archive chooser instead.</remarks>
-		public HawkFile BindFirstOf(params string[] extensions) => BindByExtensionCore(true, extensions);
+		public HawkFile BindFirstOf(string[] extensions) => BindByExtensionCore(extensions);
+
+		/// <summary>
+		/// Binds the first archive member whose file extension is <paramref name="extension"/> if one exists,
+		/// or for non-archives, binds the file if its file extension is <paramref name="extension"/>.
+		/// </summary>
+		/// <param name="extension">File extension; include the leading period, and use lowercase.</param>
+		/// <remarks>You probably should use <see cref="BindSoleItemOf"/> or the archive chooser instead.</remarks>
+		public HawkFile BindFirstOf(string extension) => BindByExtensionCore(new[] { extension });
 
 		/// <summary>causes the root to be bound (in the case of non-archive files)</summary>
 		private void BindRoot()
@@ -223,8 +231,9 @@ namespace BizHawk.Common
 			Debug.WriteLine($"{nameof(HawkFile)} bound {CanonicalFullPath}");
 		}
 
-		/// <summary>binds one of the supplied extensions if there is only one match in the archive</summary>
-		public HawkFile BindSoleItemOf(params string[] extensions) => BindByExtensionCore(false, extensions);
+		/// <summary>As <see cref="BindFirstOf(string[])"/>, but doesn't bind anything if there are multiple archive members with a matching file extension.</summary>
+		/// <param name="extensions">File extensions; include the leading period in each, and use lowercase.</param>
+		public HawkFile BindSoleItemOf(string[] extensions) => BindByExtensionCore(extensions, onlyBindSingle: true);
 
 		public void Dispose()
 		{