diff --git a/src/SharpCompress/Compressors/PPMd/PpmdStream.cs b/src/SharpCompress/Compressors/PPMd/PpmdStream.cs
index b48cf4cf..744682c4 100644
--- a/src/SharpCompress/Compressors/PPMd/PpmdStream.cs
+++ b/src/SharpCompress/Compressors/PPMd/PpmdStream.cs
@@ -28,7 +28,16 @@ public class PpmdStream : Stream, IAsyncDisposable
         _stream = stream;
         _compress = compress;
 
-        InitializeSync(stream, compress);
+        try
+        {
+            InitializeSync(stream, compress);
+        }
+        catch
+        {
+            // Construction has not transferred ownership to a caller yet.
+            _modelH?.Dispose();
+            throw;
+        }
     }
 
     private PpmdStream(
@@ -47,6 +56,13 @@ public class PpmdStream : Stream, IAsyncDisposable
 
     private void InitializeSync(Stream stream, bool compress)
     {
+        if (
+            compress
+            && (_properties.Version == PpmdVersion.H || _properties.Version == PpmdVersion.H7Z)
+        )
+        {
+            throw new NotImplementedException("PPMd H/H7Z compression not supported");
+        }
         if (_properties.Version == PpmdVersion.I1)
         {
             _model = new Model();
@@ -62,19 +78,11 @@ public class PpmdStream : Stream, IAsyncDisposable
         if (_properties.Version == PpmdVersion.H)
         {
             _modelH = new ModelPpm();
-            if (compress)
-            {
-                throw new NotImplementedException();
-            }
             _modelH.DecodeInit(stream, _properties.ModelOrder, _properties.AllocatorSize);
         }
         if (_properties.Version == PpmdVersion.H7Z)
         {
             _modelH = new ModelPpm();
-            if (compress)
-            {
-                throw new NotImplementedException();
-            }
             _modelH.DecodeInit(null, _properties.ModelOrder, _properties.AllocatorSize);
             _decoder = new Decoder();
             _decoder.Init(stream);
diff --git a/src/SharpCompress/Compressors/Squeezed/SqueezedStream.Async.cs b/src/SharpCompress/Compressors/Squeezed/SqueezedStream.Async.cs
index cfdd0e52..c4fd5854 100644
--- a/src/SharpCompress/Compressors/Squeezed/SqueezedStream.Async.cs
+++ b/src/SharpCompress/Compressors/Squeezed/SqueezedStream.Async.cs
@@ -17,11 +17,20 @@ public partial class SqueezeStream
     )
     {
         var squeezeStream = new SqueezeStream(stream, compressedSize);
-        squeezeStream._decodedStream = await squeezeStream
-            .BuildDecodedStreamAsync(cancellationToken)
-            .ConfigureAwait(false);
-
-        return squeezeStream;
+        try
+        {
+            squeezeStream._decodedStream = await squeezeStream
+                .BuildDecodedStreamAsync(cancellationToken)
+                .ConfigureAwait(false);
+            return squeezeStream;
+        }
+        catch
+        {
+#pragma warning disable VSTHRD103 // Cleanup only releases in-memory buffers; the source remains open.
+            squeezeStream.Dispose();
+#pragma warning restore VSTHRD103
+            throw;
+        }
     }
 
     public override async Task<int> ReadAsync(
@@ -83,7 +92,7 @@ public partial class SqueezeStream
         }
 
         var bitReader = new BitReader(_stream);
-        var huffmanDecoded = new PooledMemoryStream();
+        var huffmanDecoded = _huffmanDecoded = new PooledMemoryStream();
         int i = 0;
 
         while (true)
diff --git a/src/SharpCompress/Compressors/Squeezed/SqueezedStream.cs b/src/SharpCompress/Compressors/Squeezed/SqueezedStream.cs
index f6a40f1c..b3c116b2 100644
--- a/src/SharpCompress/Compressors/Squeezed/SqueezedStream.cs
+++ b/src/SharpCompress/Compressors/Squeezed/SqueezedStream.cs
@@ -16,6 +16,7 @@ public partial class SqueezeStream : Stream
     private const int SPEOF = 256;
 
     private Stream _decodedStream = null!;
+    private PooledMemoryStream? _huffmanDecoded;
 
     private SqueezeStream(Stream stream, int compressedSize)
     {
@@ -25,15 +26,36 @@ public partial class SqueezeStream : Stream
     public static SqueezeStream Create(Stream stream, int compressedSize)
     {
         var squeezeStream = new SqueezeStream(stream, compressedSize);
-        squeezeStream._decodedStream = squeezeStream.BuildDecodedStream();
-
-        return squeezeStream;
+        try
+        {
+            squeezeStream._decodedStream = squeezeStream.BuildDecodedStream();
+            return squeezeStream;
+        }
+        catch
+        {
+            squeezeStream.Dispose();
+            throw;
+        }
     }
 
     protected override void Dispose(bool disposing)
     {
-        _decodedStream?.Dispose();
-        base.Dispose(disposing);
+        try
+        {
+            if (disposing)
+            {
+                _decodedStream?.Dispose();
+            }
+        }
+        finally
+        {
+            if (disposing)
+            {
+                // RunLength90Stream deliberately does not own its input.
+                _huffmanDecoded?.Dispose();
+            }
+            base.Dispose(disposing);
+        }
     }
 
     public override bool CanRead => true;
@@ -79,7 +101,7 @@ public partial class SqueezeStream : Stream
         }
 
         var bitReader = new BitReader(_stream);
-        var huffmanDecoded = new PooledMemoryStream();
+        var huffmanDecoded = _huffmanDecoded = new PooledMemoryStream();
         int i = 0;
 
         while (true)
diff --git a/tests/SharpCompress.Test/Streams/SqueezeLifetimeTests.cs b/tests/SharpCompress.Test/Streams/SqueezeLifetimeTests.cs
new file mode 100644
index 00000000..b5a58aa5
--- /dev/null
+++ b/tests/SharpCompress.Test/Streams/SqueezeLifetimeTests.cs
@@ -0,0 +1,42 @@
+using System;
+using System.IO;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
+using SharpCompress.Compressors.PPMd;
+using SharpCompress.Compressors.Squeezed;
+using Xunit;
+
+namespace SharpCompress.Test.Streams;
+
+public class SqueezeLifetimeTests
+{
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task DisposeReleasesOwnedHuffmanStream(bool asyncOpen)
+    {
+        // One Huffman node: literal A on zero, end marker on one.
+        using var source = new MemoryStream(new byte[] { 1, 0, 190, 255, 255, 254, 2 });
+        var stream = asyncOpen
+            ? await SqueezeStream.CreateAsync(source, 7, CancellationToken.None)
+            : SqueezeStream.Create(source, 7);
+        var owned = (Stream)
+            typeof(SqueezeStream)
+                .GetField("_huffmanDecoded", BindingFlags.Instance | BindingFlags.NonPublic)!
+                .GetValue(stream)!;
+        Assert.True(owned.CanRead);
+        stream.Dispose();
+        Assert.False(owned.CanRead);
+        Assert.True(source.CanRead);
+    }
+
+    [Fact]
+    public void UnsupportedPpmdCompressionLeavesInputOpen()
+    {
+        using var source = new MemoryStream();
+        var properties = new PpmdProperties(new byte[] { 2, 0, 0, 16, 0 });
+        Assert.Throws<NotImplementedException>(() => PpmdStream.Create(properties, source, true));
+        Assert.True(source.CanRead);
+    }
+}