diff --git a/gunicorn/util.py b/gunicorn/util.py
index 11e285d5..d5730105 100644
--- a/gunicorn/util.py
+++ b/gunicorn/util.py
@@ -279,6 +279,40 @@ def close(sock):
         pass
 
 
+def close_graceful(sock, timeout=2.0, max_drain=65536):
+    """Close a TCP socket following RFC 9112 section 9.6.
+
+    Half-closes the write side to send FIN, then lingers on the read side
+    to drain the kernel recv buffer until the peer closes or a cap is hit,
+    then fully closes. This avoids the kernel sending RST (truncating the
+    last response segment) when unread request data remains in the buffer.
+    """
+    try:
+        try:
+            sock.shutdown(socket.SHUT_WR)
+        except OSError:
+            return
+        deadline = time.monotonic() + timeout
+        drained = 0
+        while drained < max_drain:
+            remaining = deadline - time.monotonic()
+            if remaining <= 0:
+                break
+            try:
+                sock.settimeout(remaining)
+                data = sock.recv(4096)
+            except (socket.timeout, OSError):
+                break
+            if not data:
+                break
+            drained += len(data)
+    finally:
+        try:
+            sock.close()
+        except OSError:
+            pass
+
+
 try:
     from os import closerange
 except ImportError:
diff --git a/gunicorn/workers/gthread.py b/gunicorn/workers/gthread.py
index 490d1ad0..cd5f86f5 100644
--- a/gunicorn/workers/gthread.py
+++ b/gunicorn/workers/gthread.py
@@ -15,7 +15,6 @@ import errno
 import os
 import queue
 import selectors
-import socket
 import ssl
 import sys
 import time
@@ -121,8 +120,12 @@ class TConn:
         finally:
             sel.close()
 
-    def close(self):
-        util.close(self.sock)
+    def close(self, graceful=False):
+        if graceful:
+            self.sock.setblocking(True)
+            util.close_graceful(self.sock)
+        else:
+            util.close(self.sock)
 
 
 class PollableMethodQueue:
@@ -435,7 +438,7 @@ class ThreadWorker(base.Worker):
                                      partial(self.on_client_socket_readable, conn))
             else:
                 self.nr_conns -= 1
-                conn.close()
+                conn.close(graceful=True)
         except Exception:
             self.nr_conns -= 1
             conn.close()
@@ -693,11 +696,7 @@ class ThreadWorker(base.Worker):
                 # If the requests have already been sent, we should close the
                 # connection to indicate the error.
                 self.log.exception("Error handling request")
-                try:
-                    conn.sock.shutdown(socket.SHUT_RDWR)
-                    conn.sock.close()
-                except OSError:
-                    pass
+                util.close_graceful(conn.sock)
                 raise StopIteration()
             raise
         finally:
diff --git a/gunicorn/workers/sync.py b/gunicorn/workers/sync.py
index 763f8652..dc731060 100644
--- a/gunicorn/workers/sync.py
+++ b/gunicorn/workers/sync.py
@@ -7,7 +7,6 @@ from datetime import datetime
 import errno
 import os
 import select
-import socket
 import ssl
 import sys
 
@@ -164,7 +163,7 @@ class SyncWorker(base.Worker):
         except BaseException as e:
             self.handle_error(req, client, addr, e)
         finally:
-            util.close(client)
+            util.close_graceful(client)
 
     def handle_request(self, listener, req, client, addr):
         environ = {}
@@ -203,11 +202,7 @@ class SyncWorker(base.Worker):
                 # If the requests have already been sent, we should close the
                 # connection to indicate the error.
                 self.log.exception("Error handling request")
-                try:
-                    client.shutdown(socket.SHUT_RDWR)
-                    client.close()
-                except OSError:
-                    pass
+                util.close_graceful(client)
                 raise StopIteration()
             raise
         finally: