diff --git a/jetty-http3/http3-client/src/main/java/org/eclipse/jetty/http3/client/internal/ClientHTTP3Session.java b/jetty-http3/http3-client/src/main/java/org/eclipse/jetty/http3/client/internal/ClientHTTP3Session.java
index 4143fb56139..29d2832ed91 100644
--- a/jetty-http3/http3-client/src/main/java/org/eclipse/jetty/http3/client/internal/ClientHTTP3Session.java
+++ b/jetty-http3/http3-client/src/main/java/org/eclipse/jetty/http3/client/internal/ClientHTTP3Session.java
@@ -184,7 +184,7 @@ public class ClientHTTP3Session extends ClientProtocolSession
             else if (key == SettingsFrame.MAX_FIELD_SECTION_SIZE)
             {
                 // Must cap the maxHeaderSize to avoid large allocations.
-                int maxHeadersSize = (int)Math.min(value, configuration.getMaxResponseHeadersSize());
+                int maxHeadersSize = (int)Math.min(value, configuration.getMaxRequestHeadersSize());
                 encoder.setMaxHeadersSize(maxHeadersSize);
             }
             else if (key == SettingsFrame.MAX_BLOCKED_STREAMS)
diff --git a/jetty-http3/http3-tests/src/test/java/org/eclipse/jetty/http3/tests/ClientServerTest.java b/jetty-http3/http3-tests/src/test/java/org/eclipse/jetty/http3/tests/ClientServerTest.java
index d17576398cb..7b6984452a4 100644
--- a/jetty-http3/http3-tests/src/test/java/org/eclipse/jetty/http3/tests/ClientServerTest.java
+++ b/jetty-http3/http3-tests/src/test/java/org/eclipse/jetty/http3/tests/ClientServerTest.java
@@ -373,13 +373,22 @@ public class ClientServerTest extends AbstractClientServerTest
             }
         });
 
-        int maxRequestHeadersSize = 128;
+        int maxRequestHeadersSize = 256;
         HTTP3Configuration http3Configuration = http3Client.getHTTP3Configuration();
         http3Configuration.setMaxRequestHeadersSize(maxRequestHeadersSize);
         // Disable the dynamic table, otherwise the large header
-        // is sent as string literal on the encoder stream.
+        // is sent as string literal on the encoder stream, rather than the message stream.
         http3Configuration.setMaxEncoderTableCapacity(0);
-        Session.Client clientSession = newSession(new Session.Client.Listener() {});
+        CountDownLatch settingsLatch = new CountDownLatch(1);
+        Session.Client clientSession = newSession(new Session.Client.Listener()
+        {
+            @Override
+            public void onSettings(Session session, SettingsFrame frame)
+            {
+                settingsLatch.countDown();
+            }
+        });
+        assertTrue(settingsLatch.await(5, TimeUnit.SECONDS));
 
         CountDownLatch requestFailureLatch = new CountDownLatch(1);
         HttpFields largeHeaders = HttpFields.build().put("too-large", "x".repeat(2 * maxRequestHeadersSize));
@@ -413,7 +422,7 @@ public class ClientServerTest extends AbstractClientServerTest
     @Test
     public void testResponseHeadersTooLarge() throws Exception
     {
-        int maxResponseHeadersSize = 128;
+        int maxResponseHeadersSize = 256;
         CountDownLatch settingsLatch = new CountDownLatch(2);
         AtomicReference<Session> serverSessionRef = new AtomicReference<>();
         CountDownLatch responseFailureLatch = new CountDownLatch(1);
@@ -458,7 +467,7 @@ public class ClientServerTest extends AbstractClientServerTest
         assertNotNull(h3);
         HTTP3Configuration http3Configuration = h3.getHTTP3Configuration();
         // Disable the dynamic table, otherwise the large header
-        // is sent as string literal on the encoder stream.
+        // is sent as string literal on the encoder stream, rather than the message stream.
         http3Configuration.setMaxEncoderTableCapacity(0);
         http3Configuration.setMaxResponseHeadersSize(maxResponseHeadersSize);
 
@@ -519,10 +528,10 @@ public class ClientServerTest extends AbstractClientServerTest
                     @Override
                     public void onDataAvailable(Stream.Server stream)
                     {
-                        // TODO: we should not be needing this!!!
+                        // Calling readData() triggers the read+parse
+                        // of the trailer, and returns no data.
                         Stream.Data data = stream.readData();
                         assertNull(data);
-                        stream.demand();
                     }
 
                     @Override
diff --git a/jetty-quic/quic-quiche/quic-quiche-jna/src/main/java/org/eclipse/jetty/quic/quiche/jna/JnaQuicheConnection.java b/jetty-quic/quic-quiche/quic-quiche-jna/src/main/java/org/eclipse/jetty/quic/quiche/jna/JnaQuicheConnection.java
index ca150fe7695..5a4f980df8a 100644
--- a/jetty-quic/quic-quiche/quic-quiche-jna/src/main/java/org/eclipse/jetty/quic/quiche/jna/JnaQuicheConnection.java
+++ b/jetty-quic/quic-quiche/quic-quiche-jna/src/main/java/org/eclipse/jetty/quic/quiche/jna/JnaQuicheConnection.java
@@ -690,7 +690,7 @@ public class JnaQuicheConnection extends QuicheConnection
         {
             if (quicheConn == null)
                 throw new IOException("connection was released");
-            int written = LibQuiche.INSTANCE.quiche_conn_stream_send(quicheConn, new uint64_t(streamId), buffer, new size_t(buffer.remaining()), last).intValue();
+            int written = LibQuiche.INSTANCE.quiche_conn_stream_send(quicheConn, new uint64_t(streamId), jnaBuffer(buffer), new size_t(buffer.remaining()), last).intValue();
             if (written == quiche_error.QUICHE_ERR_DONE)
                 return 0;
             if (written < 0L)
@@ -700,6 +700,35 @@ public class JnaQuicheConnection extends QuicheConnection
         }
     }
 
+    /**
+     * JNA requires ByteBuffers that are either direct or backed by an array.
+     * Read-only heap buffer are not direct and are considered not backed by an
+     * array, so buffer.hasArray() returns false for then an JNA rejects them
+     * by throwing IllegalStateException with the message <code>"Buffer arguments
+     * must be direct or have a primitive backing array"</code> from this native
+     * method in <code>dispatch.c:615</code>:
+     * <pre>
+     * static void
+     * dispatch(JNIEnv *env, void* func, jint flags, jobjectArray args,
+     *          ffi_type *return_type, void *presult)
+     * </pre>
+     * so this method ensures the buffer fulfils JNA's conditions, or it copies
+     * the given buffer into a new heap buffer and returns the copy, while also
+     * keeping the limit and position of the original buffer and setting them
+     * on the new buffer in a way comparable to the original buffer's.
+     */
+    private static ByteBuffer jnaBuffer(ByteBuffer buffer)
+    {
+        if (buffer.isDirect() || buffer.hasArray())
+            return buffer;
+        ByteBuffer jnaBuffer = ByteBuffer.allocate(buffer.remaining());
+        int oldPosition = buffer.position();
+        jnaBuffer.put(buffer);
+        jnaBuffer.flip();
+        buffer.position(oldPosition);
+        return jnaBuffer;
+    }
+
     @Override
     public int drainClearBytesForStream(long streamId, ByteBuffer buffer) throws IOException
     {