diff --git a/src/Glyph11/Parser/FlexibleParser/FlexibleParser.TryExtractFullHeader.cs b/src/Glyph11/Parser/FlexibleParser/FlexibleParser.TryExtractFullHeader.cs
index c599e14..18eb1ce 100644
--- a/src/Glyph11/Parser/FlexibleParser/FlexibleParser.TryExtractFullHeader.cs
+++ b/src/Glyph11/Parser/FlexibleParser/FlexibleParser.TryExtractFullHeader.cs
@@ -9,8 +9,8 @@ public static partial class FlexibleParser
     /// Entry point: tries to extract a complete HTTP/1.1 header block (request line + headers).
     /// <para>
     /// Single-segment input is dispatched to the zero-copy ROM path.
-    /// Multi-segment input is checked for completeness (<c>\r\n\r\n</c>), then linearized
-    /// via <c>ToArray()</c> and parsed through the ROM path.
+    /// Multi-segment input is checked for completeness (<c>\r\n\r\n</c>), then its header block
+    /// alone is linearized (a pipelined body is never copied) and parsed through the ROM path.
     /// </para>
     /// </summary>
     /// <param name="input">Input buffer from the network layer.</param>
@@ -36,8 +36,9 @@ public static bool TryParseRequestHeader(ref ReadOnlySequence<byte> input, Binar
             return false;
         }
 
-        // Linearize: copy all segments into a single contiguous array, then parse via ROM
-        ReadOnlyMemory<byte> mem = input.ToArray();
+        // Linearize the header block only — never the pipelined body behind it.
+        // reader.Consumed is the block's length, CRLFCRLF included.
+        ReadOnlyMemory<byte> mem = input.Slice(0, reader.Consumed).ToArray();
         return TryParseRequestHeader(ref mem, request, out consumed);
     }
 }
diff --git a/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullHeader.cs b/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullHeader.cs
index ed6fe80..e89a868 100644
--- a/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullHeader.cs
+++ b/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullHeader.cs
@@ -9,8 +9,9 @@ public static partial class UltraHardenedParser
     /// Entry point: combined parse + semantic validation with full security checks.
     /// <para>
     /// Single-segment input is dispatched to the zero-copy validated ROM path.
-    /// Multi-segment input is checked for completeness (<c>\r\n\r\n</c>), then linearized
-    /// via <c>ToArray()</c> and parsed through the validated ROM path.
+    /// Multi-segment input is checked for completeness (<c>\r\n\r\n</c>) and against
+    /// <see cref="ParserLimits.MaxTotalHeaderBytes"/>, then its header block alone is linearized
+    /// (a pipelined body is never copied) and parsed through the validated ROM path.
     /// </para>
     /// </summary>
     /// <param name="input">Input buffer from the network layer.</param>
@@ -40,8 +41,12 @@ public static bool TryParseRequestHeader(
             return false;
         }
 
-        // Linearize: copy all segments into a single contiguous array, then parse via ROM
-        ReadOnlyMemory<byte> mem = input.ToArray();
+        // Linearize the header block only — never the pipelined body behind it — and only once it
+        // is known to fit: reader.Consumed is the block's length, CRLFCRLF included.
+        if (reader.Consumed > limits.MaxTotalHeaderBytes)
+            throw new HttpParseException("Total header size exceeds limit.", statusCode: 431);
+
+        ReadOnlyMemory<byte> mem = input.Slice(0, reader.Consumed).ToArray();
         return TryParseRequestHeader(ref mem, request, in limits, out consumed);
     }
 }
diff --git a/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullResponseHeader.cs b/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullResponseHeader.cs
index 9416cec..6bd1ea8 100644
--- a/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullResponseHeader.cs
+++ b/src/Glyph11/Parser/UltraHardened/UltraHardenedParser.TryExtractFullResponseHeader.cs
@@ -10,8 +10,9 @@ public static partial class UltraHardenedParser
     /// checks.
     /// <para>
     /// Single-segment input is dispatched to the zero-copy validated ROM path.
-    /// Multi-segment input is checked for completeness (<c>\r\n\r\n</c>), then linearized
-    /// via <c>ToArray()</c> and parsed through the validated ROM path.
+    /// Multi-segment input is checked for completeness (<c>\r\n\r\n</c>) and against
+    /// <see cref="ParserLimits.MaxTotalHeaderBytes"/>, then its header block alone is linearized
+    /// (the body is never copied) and parsed through the validated ROM path.
     /// </para>
     /// </summary>
     /// <param name="input">Input buffer from the network layer.</param>
@@ -47,8 +48,12 @@ public static bool TryParseResponseHeader(
             return false;
         }
 
-        // Linearize: copy all segments into a single contiguous array, then parse via ROM
-        ReadOnlyMemory<byte> mem = input.ToArray();
+        // Linearize the header block only — never the body behind it — and only once it is known
+        // to fit: reader.Consumed is the block's length, CRLFCRLF included.
+        if (reader.Consumed > limits.MaxTotalHeaderBytes)
+            throw new HttpParseException("Total header size exceeds limit.", statusCode: 431);
+
+        ReadOnlyMemory<byte> mem = input.Slice(0, reader.Consumed).ToArray();
         return TryParseResponseHeader(ref mem, response, in limits, out consumed);
     }
 }
diff --git a/tests/Tests/MultiSegment.HeaderCopy.cs b/tests/Tests/MultiSegment.HeaderCopy.cs
new file mode 100644
index 0000000..a434670
--- /dev/null
+++ b/tests/Tests/MultiSegment.HeaderCopy.cs
@@ -0,0 +1,252 @@
+using System.Buffers;
+using System.Runtime.InteropServices;
+using System.Text;
+using Glyph11;
+using Glyph11.Parser;
+using Glyph11.Parser.FlexibleParser;
+using Glyph11.Parser.UltraHardened;
+using Glyph11.Protocol;
+using Glyph11.Utils;
+
+namespace Tests;
+
+/// <summary>
+/// Multi-segment input is linearized before parsing. Only the header block may be copied — a
+/// pipelined body behind it never — and the header limit is checked before anything is copied
+/// (issue #65).
+/// </summary>
+public class MultiSegmentHeaderCopyTests : IDisposable
+{
+    private const int BodySize = 8 * 1024 * 1024;
+
+    private const string RequestHeader =
+        "POST /upload?x=1 HTTP/1.1\r\nHost: example.com\r\nContent-Length: 8388608\r\n\r\n";
+
+    private const string ResponseHeader =
+        "HTTP/1.1 200 OK\r\nContent-Length: 8388608\r\n\r\n";
+
+    private readonly BinaryRequest _request = new();
+    private readonly BinaryResponse _response = new();
+
+    public void Dispose()
+    {
+        _request.Dispose();
+        _response.Dispose();
+        GC.SuppressFinalize(this);
+    }
+
+    // ================================================================
+    // UltraHardenedParser — requests
+    // ================================================================
+
+    [Fact]
+    public void Request_PipelinedBody_IsNotCopied()
+    {
+        var limits = ParserLimits.Default;
+        var seq = HeaderThenBody(RequestHeader, BodySize);
+
+        WarmUp(() =>
+        {
+            var warm = HeaderThenBody(RequestHeader, 16);
+            UltraHardenedParser.TryExtractFullHeaderValidated(ref warm, _request, in limits, out _);
+        });
+        _request.Clear();
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        bool ok = UltraHardenedParser.TryExtractFullHeaderValidated(ref seq, _request, in limits, out int bytesRead);
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.True(ok);
+        Assert.Equal(RequestHeader.Length - 1, bytesRead);
+        AssertAscii.Equal("POST", _request.Method);
+        AssertAscii.Equal("/upload", _request.Path);
+        Assert.Equal(2, _request.Headers.Count);
+        AssertAscii.Equal("Content-Length", _request.Headers[1].Key);
+
+        Assert.Equal(RequestHeader.Length, BackingArrayLength(_request.Method));
+        Assert.True(allocated < 64 * 1024, $"allocated {allocated} bytes for an {BodySize}-byte pipelined body");
+    }
+
+    [Theory]
+    [InlineData(1)]   // terminator split as "\r" | "\n\r\n"
+    [InlineData(2)]   // "\r\n" | "\r\n"
+    [InlineData(3)]   // "\r\n\r" | "\n"
+    public void Request_TerminatorSplitAcrossSegments_CopiesExactlyTheHeaderBlock(int splitInsideTerminator)
+    {
+        var limits = ParserLimits.Default;
+        int cut = RequestHeader.Length - 4 + splitInsideTerminator;
+        var bytes = Encoding.ASCII.GetBytes(RequestHeader + "BODYBODYBODY");
+        var seq = Segments(bytes[..cut], bytes[cut..]);
+
+        Assert.True(UltraHardenedParser.TryExtractFullHeaderValidated(ref seq, _request, in limits, out int bytesRead));
+        Assert.Equal(RequestHeader.Length - 1, bytesRead);
+        Assert.Equal(RequestHeader.Length, BackingArrayLength(_request.Path));
+    }
+
+    [Fact]
+    public void Request_BodyStartingInTheTerminatorsSegment_IsNotCopied()
+    {
+        var limits = ParserLimits.Default;
+        var head = Encoding.ASCII.GetBytes(RequestHeader);
+        var seq = Segments(head[..20], [.. head[20..], .. "partial body"u8.ToArray()], new byte[4096]);
+
+        Assert.True(UltraHardenedParser.TryExtractFullHeaderValidated(ref seq, _request, in limits, out int bytesRead));
+        Assert.Equal(RequestHeader.Length - 1, bytesRead);
+        Assert.Equal(RequestHeader.Length, BackingArrayLength(_request.Method));
+    }
+
+    [Fact]
+    public void Request_HeaderOverLimit_Throws431_BeforeCopying()
+    {
+        var limits = ParserLimits.Default with { MaxTotalHeaderBytes = RequestHeader.Length - 1 };
+        var seq = HeaderThenBody(RequestHeader, BodySize);
+
+        WarmUp(() =>
+        {
+            var warm = HeaderThenBody(RequestHeader, 16);
+            try { UltraHardenedParser.TryExtractFullHeaderValidated(ref warm, _request, in limits, out _); }
+            catch (HttpParseException) { }
+        });
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        var ex = Assert.Throws<HttpParseException>(
+            () => UltraHardenedParser.TryExtractFullHeaderValidated(ref seq, _request, in limits, out _));
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.Equal(431, ex.StatusCode);
+        Assert.True(allocated < 1024 * 1024, $"allocated {allocated} bytes before rejecting");
+    }
+
+    [Fact]
+    public void Request_HeaderExactlyAtLimit_Parses()
+    {
+        var limits = ParserLimits.Default with { MaxTotalHeaderBytes = RequestHeader.Length };
+        var seq = HeaderThenBody(RequestHeader, 1024);
+
+        Assert.True(UltraHardenedParser.TryExtractFullHeaderValidated(ref seq, _request, in limits, out int bytesRead));
+        Assert.Equal(RequestHeader.Length - 1, bytesRead);
+    }
+
+    // ================================================================
+    // UltraHardenedParser — responses
+    // ================================================================
+
+    [Fact]
+    public void Response_Body_IsNotCopied()
+    {
+        var limits = ParserLimits.Default;
+        var seq = HeaderThenBody(ResponseHeader, BodySize);
+
+        WarmUp(() =>
+        {
+            var warm = HeaderThenBody(ResponseHeader, 16);
+            UltraHardenedParser.TryExtractFullResponseHeaderValidated(ref warm, _response, in limits, out _);
+        });
+        _response.Clear();
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        bool ok = UltraHardenedParser.TryExtractFullResponseHeaderValidated(ref seq, _response, in limits, out int bytesRead);
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.True(ok);
+        Assert.Equal(ResponseHeader.Length - 1, bytesRead);
+        Assert.Equal(200, _response.Status);
+        AssertAscii.Equal("OK", _response.ReasonPhrase);
+
+        Assert.Equal(ResponseHeader.Length, BackingArrayLength(_response.Version));
+        Assert.True(allocated < 64 * 1024, $"allocated {allocated} bytes for an {BodySize}-byte body");
+    }
+
+    [Fact]
+    public void Response_HeaderOverLimit_Throws431_BeforeCopying()
+    {
+        var limits = ParserLimits.Default with { MaxTotalHeaderBytes = ResponseHeader.Length - 1 };
+        var seq = HeaderThenBody(ResponseHeader, BodySize);
+
+        WarmUp(() =>
+        {
+            var warm = HeaderThenBody(ResponseHeader, 16);
+            try { UltraHardenedParser.TryExtractFullResponseHeaderValidated(ref warm, _response, in limits, out _); }
+            catch (HttpParseException) { }
+        });
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        var ex = Assert.Throws<HttpParseException>(
+            () => UltraHardenedParser.TryExtractFullResponseHeaderValidated(ref seq, _response, in limits, out _));
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.Equal(431, ex.StatusCode);
+        Assert.True(allocated < 1024 * 1024, $"allocated {allocated} bytes before rejecting");
+    }
+
+    // ================================================================
+    // FlexibleParser
+    // ================================================================
+
+    [Fact]
+    public void Flexible_PipelinedBody_IsNotCopied()
+    {
+        var seq = HeaderThenBody(RequestHeader, BodySize);
+
+        WarmUp(() =>
+        {
+            var warm = HeaderThenBody(RequestHeader, 16);
+            FlexibleParser.TryExtractFullHeader(ref warm, _request, out _);
+        });
+        _request.Clear();
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        bool ok = FlexibleParser.TryExtractFullHeader(ref seq, _request, out int bytesRead);
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.True(ok);
+        Assert.Equal(RequestHeader.Length - 1, bytesRead);
+        AssertAscii.Equal("/upload", _request.Path);
+        Assert.Equal(2, _request.Headers.Count);
+
+        Assert.Equal(RequestHeader.Length, BackingArrayLength(_request.Method));
+        Assert.True(allocated < 64 * 1024, $"allocated {allocated} bytes for an {BodySize}-byte pipelined body");
+    }
+
+    // ================================================================
+    // Helpers
+    // ================================================================
+
+    private static void WarmUp(Action action)
+    {
+        // First calls JIT and initialize statics; keep that out of the allocation measurements.
+        action();
+        action();
+    }
+
+    private static int BackingArrayLength(ReadOnlyMemory<byte> slice)
+    {
+        Assert.True(MemoryMarshal.TryGetArray(slice, out ArraySegment<byte> segment));
+        return segment.Array!.Length;
+    }
+
+    /// <summary>
+    /// The header split across two segments, then <paramref name="bodySize"/> body bytes in
+    /// 1 MiB segments.
+    /// </summary>
+    private static ReadOnlySequence<byte> HeaderThenBody(string header, int bodySize)
+    {
+        var head = Encoding.ASCII.GetBytes(header);
+        var parts = new List<byte[]> { head[..(head.Length / 2)], head[(head.Length / 2)..] };
+
+        for (int remaining = bodySize; remaining > 0; remaining -= 1024 * 1024)
+            parts.Add(new byte[Math.Min(remaining, 1024 * 1024)]);
+
+        return Segments([.. parts]);
+    }
+
+    private static ReadOnlySequence<byte> Segments(params byte[][] parts)
+    {
+        var first = new BufferSegment(parts[0]);
+        var last = first;
+        for (int i = 1; i < parts.Length; i++)
+            last = last.Append(parts[i]);
+
+        return new ReadOnlySequence<byte>(first, 0, last, last.Memory.Length);
+    }
+}