diff --git a/src/BizHawk.Common/checksums/SHA1Checksum.cs b/src/BizHawk.Common/checksums/SHA1Checksum.cs
index 88c2b46b02..ba14e9a45c 100644
--- a/src/BizHawk.Common/checksums/SHA1Checksum.cs
+++ b/src/BizHawk.Common/checksums/SHA1Checksum.cs
@@ -7,40 +7,6 @@ using BizHawk.Common.BufferExtensions;
 
 namespace BizHawk.Common
 {
-	public interface ISHA1
-	{
-		byte[] ComputeHash(byte[] buffer);
-	}
-
-	public sealed class NETSHA1 : ISHA1
-	{
-		private readonly SHA1 _sha1Impl;
-
-		public NETSHA1()
-		{
-			_sha1Impl = SHA1.Create();
-			Debug.Assert(_sha1Impl.CanReuseTransform && _sha1Impl.HashSize is SHA1Checksum.EXPECTED_LENGTH);
-		}
-
-		public byte[] ComputeHash(byte[] buffer)
-			=> _sha1Impl.ComputeHash(buffer);
-	}
-
-	public sealed class FastSHA1 : ISHA1
-	{
-		public unsafe byte[] ComputeHash(byte[] buffer)
-		{
-			// Set SHA1 start state
-			var state = stackalloc uint[] { 0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0 };
-			// This will use dedicated SHA instructions, which perform 4x faster than a generic implementation
-			LibBizHash.BizCalcSha1((IntPtr)state, buffer, buffer.Length);
-			// The copy seems wasteful, but pinning the state down actually has a bigger performance impact
-			var ret = new byte[20];
-			Marshal.Copy((IntPtr)state, ret, 0, 20);
-			return ret;
-		}
-	}
-
 	/// <summary>uses <see cref="SHA1"/> implementation from BCL</summary>
 	/// <seealso cref="CRC32Checksum"/>
 	/// <seealso cref="MD5Checksum"/>
@@ -70,27 +36,49 @@ namespace BizHawk.Common
 			return impl.GetHashAndReset();
 		}
 #else
-		private static ISHA1? _sha1Impl;
+		private static unsafe byte[] UnmanagedImpl(byte[] buffer)
+		{
+			// Set SHA1 start state
+			var state = stackalloc uint[] { 0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0 };
+			// This will use dedicated SHA instructions, which perform 4x faster than a generic implementation
+			LibBizHash.BizCalcSha1((IntPtr) state, buffer, buffer.Length);
+			// The copy seems wasteful, but pinning the state down actually has a bigger performance impact
+			var ret = new byte[20];
+			Marshal.Copy((IntPtr) state, ret, 0, 20);
+			return ret;
+		}
 
-		private static ISHA1 SHA1Impl
+		private static SHA1? _sha1Impl;
+
+		private static SHA1 SHA1Impl
 		{
 			get
 			{
 				if (_sha1Impl == null)
 				{
-					_sha1Impl = LibBizHash.BizSupportsShaInstructions()
-						? new FastSHA1()
-						: new NETSHA1();
+					_sha1Impl = SHA1.Create();
+					Debug.Assert(_sha1Impl.CanReuseTransform && _sha1Impl.HashSize is EXPECTED_LENGTH);
 				}
 				return _sha1Impl;
 			}
 		}
 
 		public static byte[] Compute(byte[] data)
-			=> SHA1Impl.ComputeHash(data);
+			=> LibBizHash.BizSupportsShaInstructions()
+				? UnmanagedImpl(data)
+				: SHA1Impl.ComputeHash(data);
 
 		public static byte[] ComputeConcat(byte[] dataA, byte[] dataB)
 		{
+			if (LibBizHash.BizSupportsShaInstructions())
+			{
+				var concat = new byte[dataA.Length + dataB.Length];
+				Array.Copy(sourceArray: dataA, destinationArray: concat, length: dataA.Length);
+				Array.Copy(
+					sourceArray: dataB, sourceIndex: 0,
+					destinationArray: concat, destinationIndex: dataA.Length, length: dataB.Length);
+				return UnmanagedImpl(concat);
+			}
 			using var impl = IncrementalHash.CreateHash(HashAlgorithmName.SHA1);
 			impl.AppendData(dataA);
 			impl.AppendData(dataB);