diff --git a/SabreTools.FileTypes/Compress/SevenZip/Compress/ZSTD/ZstandardStream.cs b/SabreTools.FileTypes/Compress/SevenZip/Compress/ZSTD/ZstandardStream.cs
index 8f76ae57..71e86bf1 100644
--- a/SabreTools.FileTypes/Compress/SevenZip/Compress/ZSTD/ZstandardStream.cs
+++ b/SabreTools.FileTypes/Compress/SevenZip/Compress/ZSTD/ZstandardStream.cs
@@ -362,7 +362,6 @@ namespace Compress.SevenZip.Compress.ZSTD
                 sizeToGo -= sizenow;
             }
 
-            position += offset;
             return offset;
         }
 
diff --git a/SabreTools.FileTypes/Compress/SevenZip/SevenZip.cs b/SabreTools.FileTypes/Compress/SevenZip/SevenZip.cs
index 55565ad8..ceff7415 100644
--- a/SabreTools.FileTypes/Compress/SevenZip/SevenZip.cs
+++ b/SabreTools.FileTypes/Compress/SevenZip/SevenZip.cs
@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Security.Policy;
 using System.Text;
+using Compress.SevenZip.Compress.ZSTD;
 using Compress.SevenZip.Structure;
 using FileInfo = RVIO.FileInfo;
 
@@ -9,6 +11,14 @@ namespace Compress.SevenZip
 {
     public partial class SevenZ : ICompress
     {
+
+        public enum sevenZipCompressType
+        {
+            uncompressed,
+            lzma,
+            zstd
+        }
+
         public static bool supportZstd
         {
             get;
@@ -17,7 +27,14 @@ namespace Compress.SevenZip
 
         public static void TestForZstd()
         {
-            supportZstd = RVIO.File.Exists("libzstd.dll");
+            supportZstd = false;
+            if (Environment.OSVersion.Platform == PlatformID.Win32NT)
+            {
+                var root = Path.GetDirectoryName(typeof(ZstandardInterop).Assembly.Location);
+                var path = Environment.Is64BitProcess ? "x64" : "x86";
+                var file = Path.Combine(root, path, "libzstd.dll");
+                supportZstd = RVIO.File.Exists(file);
+            }
         }
 
 
@@ -43,7 +60,7 @@ namespace Compress.SevenZip
 
         private SignatureHeader _signatureHeader;
 
-        private bool _compressed = true;
+        private sevenZipCompressType _compressed = sevenZipCompressType.lzma;
 
 
         private long _baseOffset;
diff --git a/SabreTools.FileTypes/Compress/SevenZip/SevenZipWrite.cs b/SabreTools.FileTypes/Compress/SevenZip/SevenZipWrite.cs
index f6bea2b7..01ad80e1 100644
--- a/SabreTools.FileTypes/Compress/SevenZip/SevenZipWrite.cs
+++ b/SabreTools.FileTypes/Compress/SevenZip/SevenZipWrite.cs
@@ -1,6 +1,7 @@
 using System.IO;
 using System.Text;
 using Compress.SevenZip.Compress.LZMA;
+using Compress.SevenZip.Compress.ZSTD;
 using Compress.SevenZip.Structure;
 using Compress.Utils;
 using FileInfo = RVIO.FileInfo;
@@ -19,16 +20,21 @@ namespace Compress.SevenZip
 
         public ZipReturn ZipFileCreate(string newFilename)
         {
-            return ZipFileCreate(newFilename, true);
+            return ZipFileCreate(newFilename, sevenZipCompressType.lzma);
         }
-
-
-        public ZipReturn ZipFileCreateFromUncompressedSize(string newFilename, ulong unCompressedSize)
+        
+        public ZipReturn ZipFileCreateFromUncompressedSize(string newFilename, sevenZipCompressType ctype, ulong unCompressedSize)
         {
-            return ZipFileCreate(newFilename, true, GetDictionarySizeFromUncompressedSize(unCompressedSize));
+            if (ctype == sevenZipCompressType.zstd)
+            {
+                if (!supportZstd)
+                    ctype = sevenZipCompressType.lzma;
+            }
+
+            return ZipFileCreate(newFilename, ctype, GetDictionarySizeFromUncompressedSize(unCompressedSize));
         }
 
-        public ZipReturn ZipFileCreate(string newFilename, bool compressOutput, int dictionarySize = 1 << 24, int numFastBytes = 64)
+        public ZipReturn ZipFileCreate(string newFilename, sevenZipCompressType compressOutput, int dictionarySize = 1 << 24, int numFastBytes = 64)
         {
             if (ZipOpen != ZipOpenType.Closed)
             {
@@ -59,22 +65,21 @@ namespace Compress.SevenZip
             _compressed = compressOutput;
 
             _unpackedStreamSize = 0;
-            if (_compressed)
+            if (_compressed == sevenZipCompressType.lzma)
             {
                 LzmaEncoderProperties ep = new LzmaEncoderProperties(true, dictionarySize, numFastBytes);
                 LzmaStream lzs = new LzmaStream(ep, false, _zipFs);
                 _codeMSbytes = lzs.Properties;
                 _lzmaStream = lzs;
-
-
-                /*
-                ZstandardStream zss = new ZstandardStream(_zipFs, 22, true);
-                _codeMSbytes = new byte[] { 1, 4, 18, 0, 0 };
-                _lzmaStream = zss;
-                */
                 _packStreamStart = (ulong)_zipFs.Position;
             }
-
+            else if (_compressed == sevenZipCompressType.zstd)
+            {
+                ZstandardStream zss = new ZstandardStream(_zipFs, 18, true);
+                _codeMSbytes = new byte[] { 1, 4, 18, 0, 0 };
+                _lzmaStream = zss;
+                _packStreamStart = (ulong)_zipFs.Position;
+            }
             return ZipReturn.ZipGood;
         }
 
@@ -121,7 +126,7 @@ namespace Compress.SevenZip
             _unpackedStreamSize += uncompressedSize;
 
             _localFiles.Add(lf);
-            stream = _compressed ? _lzmaStream : _zipFs;
+            stream = _compressed == sevenZipCompressType.uncompressed ? _zipFs : _lzmaStream;
             return ZipReturn.ZipGood;
         }
 
diff --git a/SabreTools.FileTypes/Compress/SevenZip/SevenZipWriteClose.cs b/SabreTools.FileTypes/Compress/SevenZip/SevenZipWriteClose.cs
index febb1d88..3907851c 100644
--- a/SabreTools.FileTypes/Compress/SevenZip/SevenZipWriteClose.cs
+++ b/SabreTools.FileTypes/Compress/SevenZip/SevenZipWriteClose.cs
@@ -85,7 +85,7 @@ namespace Compress.SevenZip
             _header.StreamsInfo = new StreamsInfo { PackPosition = 0 };
 
             //StreamsInfo.PackedStreamsInfo
-            if (_compressed)
+            if (_compressed!=sevenZipCompressType.uncompressed)
             {
                 _header.StreamsInfo.PackedStreams = new PackedStreamInfo[1];
                 _header.StreamsInfo.PackedStreams[0] = new PackedStreamInfo { PackedSize = _packStreamSize };
@@ -105,7 +105,7 @@ namespace Compress.SevenZip
             }
             //StreamsInfo.PackedStreamsInfo, no CRC or StreamPosition required
 
-            if (_compressed)
+            if (_compressed != sevenZipCompressType.uncompressed)
             {
                 //StreamsInfo.Folders
                 _header.StreamsInfo.Folders = new Folder[1];
@@ -200,8 +200,9 @@ namespace Compress.SevenZip
 
         private void CloseWriting7Zip()
         {
-            if (_compressed)
+            if (_compressed != sevenZipCompressType.uncompressed)
             {
+                _lzmaStream.Flush();
                 _lzmaStream.Close();
             }