diff --git a/src/SharpCompress/Compressors/LZMA/LZipStream.Async.cs b/src/SharpCompress/Compressors/LZMA/LZipStream.Async.cs
index 949fbc97..36929d8a 100644
--- a/src/SharpCompress/Compressors/LZMA/LZipStream.Async.cs
+++ b/src/SharpCompress/Compressors/LZMA/LZipStream.Async.cs
@@ -129,11 +129,7 @@ public sealed partial class LZipStream
         var header = ArrayPool<byte>.Shared.Rent(6);
         try
         {
-            var n = await stream.ReadAsync(header, 0, 6, cancellationToken).ConfigureAwait(false);
-
-            // TODO: Handle reading only part of the header?
-
-            if (n != 6)
+            if (!await stream.ReadFullyAsync(header, 0, 6, cancellationToken).ConfigureAwait(false))
             {
                 return 0;
             }
@@ -148,13 +144,7 @@ public sealed partial class LZipStream
             {
                 return 0;
             }
-            var basePower = header[5] & 0x1F;
-            var subtractionNumerator = (header[5] & 0xE0) >> 5;
-            if (basePower < 4 || basePower > 30)
-            {
-                return 0;
-            }
-            return (1 << basePower) - (subtractionNumerator * (1 << (basePower - 4)));
+            return DecodeDictionarySize(header[5]);
         }
         finally
         {
diff --git a/src/SharpCompress/Compressors/LZMA/LZipStream.cs b/src/SharpCompress/Compressors/LZMA/LZipStream.cs
index f2e1abea..7379639d 100644
--- a/src/SharpCompress/Compressors/LZMA/LZipStream.cs
+++ b/src/SharpCompress/Compressors/LZMA/LZipStream.cs
@@ -253,11 +253,7 @@ public sealed partial class LZipStream : Stream, IFinishable
     {
         // Read the header
         Span<byte> header = stackalloc byte[6];
-        var n = stream.Read(header);
-
-        // TODO: Handle reading only part of the header?
-
-        if (n != 6)
+        if (!stream.ReadFully(header))
         {
             return 0;
         }
@@ -272,9 +268,18 @@ public sealed partial class LZipStream : Stream, IFinishable
         {
             return 0;
         }
-        var basePower = header[5] & 0x1F;
-        var subtractionNumerator = (header[5] & 0xE0) >> 5;
-        return (1 << basePower) - (subtractionNumerator * (1 << (basePower - 4)));
+        return DecodeDictionarySize(header[5]);
+    }
+
+    private static int DecodeDictionarySize(byte encoded)
+    {
+        var basePower = encoded & 0x1F;
+        if (basePower < 12 || basePower > 29)
+        {
+            return 0;
+        }
+        var size = (1 << basePower) - ((encoded >> 5) * (1 << (basePower - 4)));
+        return size >= 4096 ? size : 0;
     }
 
     // Async methods moved to LZipStream.Async.cs
diff --git a/tests/SharpCompress.Test/Streams/LZipHeaderReadTests.cs b/tests/SharpCompress.Test/Streams/LZipHeaderReadTests.cs
new file mode 100644
index 00000000..7d45b6c9
--- /dev/null
+++ b/tests/SharpCompress.Test/Streams/LZipHeaderReadTests.cs
@@ -0,0 +1,30 @@
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using SharpCompress.Compressors.LZMA;
+using SharpCompress.Test.Mocks;
+using Xunit;
+
+namespace SharpCompress.Test.Streams;
+
+public class LZipHeaderReadTests
+{
+    [Theory]
+    [InlineData(12, 4096)]
+    [InlineData(29, 536870912)]
+    [InlineData(11, 0)]
+    [InlineData(30, 0)]
+    [InlineData(31, 0)]
+    [InlineData(44, 0)]
+    public async Task LZip_Header_Fragmentation_And_Dictionary_Validation(int encoded, int expected)
+    {
+        byte[] header = [0x4C, 0x5A, 0x49, 0x50, 1, (byte)encoded];
+        using var sync = new ShortReadStream(new MemoryStream(header));
+        using var asyncInput = new ShortReadStream(new MemoryStream(header));
+        Assert.Equal(expected, LZipStream.ValidateAndReadSize(sync));
+        Assert.Equal(
+            expected,
+            await LZipStream.ValidateAndReadSizeAsync(asyncInput, CancellationToken.None)
+        );
+    }
+}