diff --git a/src/afd.c b/src/afd.c
index bfd68c3..a2f90ec 100644
--- a/src/afd.c
+++ b/src/afd.c
@@ -1,6 +1,7 @@
 #include "afd.h"
 #include "error.h"
 #include "nt.h"
+#include "util.h"
 #include "win.h"
 
 #define FILE_DEVICE_NETWORK 0x00000012
@@ -12,6 +13,10 @@
 
 #define IOCTL_AFD_POLL _AFD_CONTROL_CODE(AFD_POLL, METHOD_BUFFERED)
 
+#ifndef SIO_BASE_HANDLE
+#define SIO_BASE_HANDLE 0x48000022
+#endif
+
 int afd_poll(SOCKET driver_socket,
              AFD_POLL_INFO* poll_info,
              OVERLAPPED* overlapped) {
@@ -81,3 +86,85 @@ int afd_poll(SOCKET driver_socket,
   else
     return_error(-1, we_map_ntstatus_to_win_error(status));
 }
+
+static SOCKET _afd_get_base_socket(SOCKET socket) {
+  SOCKET base_socket;
+  DWORD bytes;
+
+  if (WSAIoctl(socket,
+               SIO_BASE_HANDLE,
+               NULL,
+               0,
+               &base_socket,
+               sizeof base_socket,
+               &bytes,
+               NULL,
+               NULL) == SOCKET_ERROR)
+    return_error(INVALID_SOCKET);
+
+  return base_socket;
+}
+
+static ssize_t _afd_get_protocol_info(SOCKET socket,
+                                      WSAPROTOCOL_INFOW* protocol_info) {
+  ssize_t id;
+  int opt_len;
+
+  opt_len = sizeof *protocol_info;
+  if (getsockopt(socket,
+                 SOL_SOCKET,
+                 SO_PROTOCOL_INFOW,
+                 (char*) protocol_info,
+                 &opt_len) != 0)
+    return_error(-1);
+
+  id = -1;
+  for (size_t i = 0; i < array_count(AFD_PROVIDER_GUID_LIST); i++) {
+    if (memcmp(&protocol_info->ProviderId,
+               &AFD_PROVIDER_GUID_LIST[i],
+               sizeof protocol_info->ProviderId) == 0) {
+      id = i;
+      break;
+    }
+  }
+
+  /* Check if the protocol uses an msafd socket. */
+  if (id < 0)
+    return_error(-1, ERROR_NOT_SUPPORTED);
+
+  return id;
+}
+
+EPOLL_INTERNAL ssize_t afd_get_protocol(SOCKET socket,
+                                        SOCKET* afd_socket_out,
+                                        WSAPROTOCOL_INFOW* protocol_info) {
+  ssize_t id;
+  SOCKET afd_socket;
+
+  /* Try to get protocol information, assuming that the given socket is an AFD
+   * socket. This should almost always be the case, and if it is, that saves us
+   * a call to WSAIoctl(). */
+  afd_socket = socket;
+  id = _afd_get_protocol_info(afd_socket, protocol_info);
+
+  if (id < 0) {
+    /* If getting protocol information failed, it might be due to the socket
+     * not being an AFD socket. If so, attempt to fetch the underlying base
+     * socket, then try again to obtain protocol information. If that also
+     * fails, return the *original* error. */
+    DWORD original_error = GetLastError();
+    if (original_error != ERROR_NOT_SUPPORTED)
+      return_error(-1);
+
+    afd_socket = _afd_get_base_socket(socket);
+    if (afd_socket == INVALID_SOCKET || afd_socket == socket)
+      return_error(-1, original_error);
+
+    id = _afd_get_protocol_info(afd_socket, protocol_info);
+    if (id < 0)
+      return_error(-1, original_error);
+  }
+
+  *afd_socket_out = afd_socket;
+  return id;
+}
diff --git a/src/afd.h b/src/afd.h
index 01a0a82..9f4ee52 100644
--- a/src/afd.h
+++ b/src/afd.h
@@ -3,6 +3,7 @@
 
 #include "internal.h"
 #include "ntstatus.h"
+#include "util.h"
 #include "win.h"
 
 /* clang-format off */
@@ -55,6 +56,10 @@ EPOLL_INTERNAL int afd_poll(SOCKET driver_socket,
                             AFD_POLL_INFO* poll_info,
                             OVERLAPPED* overlapped);
 
+EPOLL_INTERNAL ssize_t afd_get_protocol(SOCKET socket,
+                                        SOCKET* afd_socket_out,
+                                        WSAPROTOCOL_INFOW* protocol_info);
+
 /* clang-format off */
 
 static const GUID AFD_PROVIDER_GUID_LIST[] = {
diff --git a/src/epoll-socket.c b/src/epoll-socket.c
index dfc4d76..a7faa3b 100644
--- a/src/epoll-socket.c
+++ b/src/epoll-socket.c
@@ -10,10 +10,6 @@
 #include "poll-group.h"
 #include "port.h"
 
-#ifndef SIO_BASE_HANDLE
-#define SIO_BASE_HANDLE 0x48000022
-#endif
-
 #define _EP_EVENT_MASK 0xffff
 
 typedef struct _poll_req {
@@ -160,76 +156,48 @@ static inline void _ep_sock_free(_ep_sock_private_t* sock_private) {
   free(sock_private);
 }
 
-static int _get_related_sockets(ep_port_t* port_info,
-                                SOCKET socket,
-                                SOCKET* afd_socket_out,
-                                poll_group_t** poll_group_out) {
-  SOCKET afd_socket;
-  poll_group_t* poll_group;
-  DWORD bytes;
-
-  /* Try to obtain a base handle for the socket, so we can bypass LSPs
-   * that get in the way if we want to talk to the kernel directly. If
-   * it fails we try if we work with the original socket. Note that on
-   * windows XP/2k3 this will always fail since they don't support the
-   * SIO_BASE_HANDLE ioctl.
-   */
-  afd_socket = socket;
-  WSAIoctl(socket,
-           SIO_BASE_HANDLE,
-           NULL,
-           0,
-           &afd_socket,
-           sizeof afd_socket,
-           &bytes,
-           NULL,
-           NULL);
-
-  poll_group = ep_port_acquire_poll_group(port_info, afd_socket);
-  if (poll_group == NULL)
-    return -1;
-
-  *afd_socket_out = afd_socket;
-  *poll_group_out = poll_group;
-
-  return 0;
-}
-
-static int _ep_sock_set_socket(ep_port_t* port_info,
-                               _ep_sock_private_t* sock_private,
-                               SOCKET socket) {
-  if (socket == 0 || socket == INVALID_SOCKET)
-    return_error(-1, ERROR_INVALID_HANDLE);
-
-  assert(sock_private->afd_socket == 0);
-
-  if (_get_related_sockets(port_info,
-                           socket,
-                           &sock_private->afd_socket,
-                           &sock_private->poll_group) < 0)
-    return -1;
-
-  if (ep_port_add_socket(port_info, &sock_private->pub.tree_node, socket) < 0)
-    return -1;
-
-  return 0;
-}
-
 ep_sock_t* ep_sock_new(ep_port_t* port_info, SOCKET socket) {
-  _ep_sock_private_t* sock_private = _ep_sock_alloc();
-  if (sock_private == NULL)
+  SOCKET afd_socket;
+  ssize_t protocol_id;
+  WSAPROTOCOL_INFOW protocol_info;
+  poll_group_t* poll_group;
+  _ep_sock_private_t* sock_private;
+
+  if (socket == 0 || socket == INVALID_SOCKET)
+    return_error(NULL, ERROR_INVALID_HANDLE);
+
+  protocol_id = afd_get_protocol(socket, &afd_socket, &protocol_info);
+  if (protocol_id < 0)
     return NULL;
 
+  poll_group =
+      ep_port_acquire_poll_group(port_info, protocol_id, &protocol_info);
+  if (poll_group == NULL)
+    return NULL;
+
+  sock_private = _ep_sock_alloc();
+  if (sock_private == NULL)
+    goto err1;
+
   memset(sock_private, 0, sizeof *sock_private);
+
+  sock_private->afd_socket = afd_socket;
+  sock_private->poll_group = poll_group;
+
   tree_node_init(&sock_private->pub.tree_node);
   queue_node_init(&sock_private->pub.queue_node);
 
-  if (_ep_sock_set_socket(port_info, sock_private, socket) < 0) {
-    _ep_sock_free(sock_private);
-    return NULL;
-  }
+  if (ep_port_add_socket(port_info, &sock_private->pub.tree_node, socket) < 0)
+    goto err2;
 
   return &sock_private->pub;
+
+err2:
+  _ep_sock_free(sock_private);
+err1:
+  ep_port_release_poll_group(poll_group);
+
+  return NULL;
 }
 
 void ep_sock_delete(ep_port_t* port_info, ep_sock_t* sock_info) {
diff --git a/src/epoll.c b/src/epoll.c
index d39bd60..b12c55e 100644
--- a/src/epoll.c
+++ b/src/epoll.c
@@ -254,48 +254,25 @@ int ep_port_del_socket(ep_port_t* port_info, tree_node_t* tree_node) {
 
 static poll_group_allocator_t* _get_poll_group_allocator(
     ep_port_t* port_info,
-    size_t index,
+    size_t protocol_id,
     const WSAPROTOCOL_INFOW* protocol_info) {
-  poll_group_allocator_t** pga = &port_info->poll_group_allocators[index];
+  poll_group_allocator_t** pga;
 
+  assert(protocol_id < array_count(port_info->poll_group_allocators));
+
+  pga = &port_info->poll_group_allocators[protocol_id];
   if (*pga == NULL)
     *pga = poll_group_allocator_new(port_info, protocol_info);
 
   return *pga;
 }
 
-poll_group_t* ep_port_acquire_poll_group(ep_port_t* port_info, SOCKET socket) {
-  ssize_t index;
-  size_t i;
-  WSAPROTOCOL_INFOW protocol_info;
-  int len;
-  poll_group_allocator_t* pga;
-
-  /* Obtain protocol information about the socket. */
-  len = sizeof protocol_info;
-  if (getsockopt(socket,
-                 SOL_SOCKET,
-                 SO_PROTOCOL_INFOW,
-                 (char*) &protocol_info,
-                 &len) != 0)
-    return_error(NULL);
-
-  index = -1;
-  for (i = 0; i < array_count(AFD_PROVIDER_GUID_LIST); i++) {
-    if (memcmp((void*) &protocol_info.ProviderId,
-               (void*) &AFD_PROVIDER_GUID_LIST[i],
-               sizeof protocol_info.ProviderId) == 0) {
-      index = i;
-      break;
-    }
-  }
-
-  /* Check if the protocol uses an msafd socket. */
-  if (index < 0)
-    return_error(NULL, ERROR_NOT_SUPPORTED);
-
-  pga = _get_poll_group_allocator(port_info, index, &protocol_info);
-
+poll_group_t* ep_port_acquire_poll_group(
+    ep_port_t* port_info,
+    size_t protocol_id,
+    const WSAPROTOCOL_INFOW* protocol_info) {
+  poll_group_allocator_t* pga =
+      _get_poll_group_allocator(port_info, protocol_id, protocol_info);
   return poll_group_acquire(pga);
 }
 
diff --git a/src/port.h b/src/port.h
index ee84424..cf7ebcd 100644
--- a/src/port.h
+++ b/src/port.h
@@ -25,8 +25,10 @@ typedef struct ep_port {
 EPOLL_INTERNAL ep_port_t* ep_port_new(HANDLE iocp);
 EPOLL_INTERNAL int ep_port_delete(ep_port_t* port_info);
 
-EPOLL_INTERNAL poll_group_t* ep_port_acquire_poll_group(ep_port_t* port_info,
-                                                        SOCKET socket);
+EPOLL_INTERNAL poll_group_t* ep_port_acquire_poll_group(
+    ep_port_t* port_info,
+    size_t protocol_id,
+    const WSAPROTOCOL_INFOW* protocol_info);
 EPOLL_INTERNAL void ep_port_release_poll_group(poll_group_t* poll_group);
 
 EPOLL_INTERNAL int ep_port_add_socket(ep_port_t* port_info,