diff --git a/lib/internal.h b/lib/internal.h
index 7e96e8e9..07378588 100644
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -1,5 +1,5 @@
 /* nbd client library in userspace: internal definitions
- * Copyright (C) 2013-2020 Red Hat Inc.
+ * Copyright (C) 2013-2021 Red Hat Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -106,6 +106,9 @@ struct nbd_handle {
   char *tls_username;           /* Username, NULL = use current username */
   char *tls_psk_file;           /* PSK filename, NULL = no PSK */

+  /* Extended headers. */
+  bool extended_headers;        /* If we negotiated NBD_OPT_EXTENDED_HEADERS */
+
   /* Desired metadata contexts. */
   bool request_sr;
   string_vector request_meta_contexts;
@@ -242,7 +245,10 @@ struct nbd_handle {
   /* Issuing a command must use a buffer separate from sbuf, for the
    * case when we interrupt a request to service a reply.
    */
-  struct nbd_request request;
+  union {
+    struct nbd_request request;
+    struct nbd_request_ext request_ext;
+  } req;
   bool in_write_payload;
   bool in_write_shutdown;

@@ -347,7 +353,7 @@ struct command {
   uint16_t type;
   uint64_t cookie;
   uint64_t offset;
-  uint32_t count;
+  uint64_t count;
   void *data; /* Buffer for read/write */
   struct command_cb cb;
   enum state state; /* State to resume with on next POLLIN */
diff --git a/generator/states-issue-command.c b/generator/states-issue-command.c
index a8101144..7b1d6dc7 100644
--- a/generator/states-issue-command.c
+++ b/generator/states-issue-command.c
@@ -1,5 +1,5 @@
 /* nbd client library in userspace: state machine
- * Copyright (C) 2013-2020 Red Hat Inc.
+ * Copyright (C) 2013-2021 Red Hat Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -41,14 +41,23 @@ STATE_MACHINE {
     return 0;
   }

-  h->request.magic = htobe32 (NBD_REQUEST_MAGIC);
-  h->request.flags = htobe16 (cmd->flags);
-  h->request.type = htobe16 (cmd->type);
-  h->request.handle = htobe64 (cmd->cookie);
-  h->request.offset = htobe64 (cmd->offset);
-  h->request.count = htobe32 ((uint32_t) cmd->count);
-  h->wbuf = &h->request;
-  h->wlen = sizeof (h->request);
+  /* These fields are coincident between req.request and req.request_ext */
+  h->req.request.flags = htobe16 (cmd->flags);
+  h->req.request.type = htobe16 (cmd->type);
+  h->req.request.handle = htobe64 (cmd->cookie);
+  h->req.request.offset = htobe64 (cmd->offset);
+  if (h->extended_headers) {
+    h->req.request_ext.magic = htobe32 (NBD_REQUEST_EXT_MAGIC);
+    h->req.request_ext.count = htobe64 (cmd->count);
+    h->wlen = sizeof (h->req.request_ext);
+  }
+  else {
+    assert (cmd->count <= UINT32_MAX);
+    h->req.request.magic = htobe32 (NBD_REQUEST_MAGIC);
+    h->req.request.count = htobe32 (cmd->count);
+    h->wlen = sizeof (h->req.request);
+  }
+  h->wbuf = &h->req;
   if (cmd->type == NBD_CMD_WRITE || cmd->next)
     h->wflags = MSG_MORE;
   SET_NEXT_STATE (%SEND_REQUEST);
@@ -73,7 +82,7 @@ STATE_MACHINE {

   assert (h->cmds_to_issue != NULL);
   cmd = h->cmds_to_issue;
-  assert (cmd->cookie == be64toh (h->request.handle));
+  assert (cmd->cookie == be64toh (h->req.request.handle));
   if (cmd->type == NBD_CMD_WRITE) {
     h->wbuf = cmd->data;
     h->wlen = cmd->count;
@@ -119,7 +128,7 @@ STATE_MACHINE {
   assert (!h->wlen);
   assert (h->cmds_to_issue != NULL);
   cmd = h->cmds_to_issue;
-  assert (cmd->cookie == be64toh (h->request.handle));
+  assert (cmd->cookie == be64toh (h->req.request.handle));
   h->cmds_to_issue = cmd->next;
   if (h->cmds_to_issue_tail == cmd)
     h->cmds_to_issue_tail = NULL;
diff --git a/generator/states-reply-structured.c b/generator/states-reply-structured.c
index e1da850d..5524e000 100644
--- a/generator/states-reply-structured.c
+++ b/generator/states-reply-structured.c
@@ -34,7 +34,7 @@ structured_reply_in_bounds (uint64_t offset, uint32_t length,
       offset + length > cmd->offset + cmd->count) {
     set_error (0, "range of structured reply is out of bounds, "
                "offset=%" PRIu64 ", cmd->offset=%" PRIu64 ", "
-               "length=%" PRIu32 ", cmd->count=%" PRIu32 ": "
+               "length=%" PRIu32 ", cmd->count=%" PRIu64 ": "
                "this is likely to be a bug in the NBD server",
                offset, cmd->offset, length, cmd->count);
     return false;
diff --git a/lib/rw.c b/lib/rw.c
index 4ade7508..16c2e848 100644
--- a/lib/rw.c
+++ b/lib/rw.c
@@ -1,5 +1,5 @@
 /* NBD client library in userspace
- * Copyright (C) 2013-2020 Red Hat Inc.
+ * Copyright (C) 2013-2021 Red Hat Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -216,13 +216,11 @@ nbd_internal_command_common (struct nbd_handle *h,
     }
     break;

-    /* Other commands are currently limited by the 32 bit field in the
-     * command structure on the wire, but in future we hope to support
-     * 64 bit values here with a change to the NBD protocol which is
-     * being discussed upstream.
+    /* Other commands are limited by the 32 bit field in the command
+     * structure on the wire, unless extended headers were negotiated.
      */
   default:
-    if (count > UINT32_MAX) {
+    if (!h->extended_headers && count > UINT32_MAX) {
       set_error (ERANGE, "request too large: maximum request size is %" PRIu32,
                  UINT32_MAX);
       goto err;
