diff --git a/info/nbdinfo.pod b/info/nbdinfo.pod
index c47e5175..2455e1c0 100644
--- a/info/nbdinfo.pod
+++ b/info/nbdinfo.pod
@@ -86,6 +86,7 @@ the I<--json> parameter:
    "protocol": "newstyle-fixed",
    "TLS": false,
    "structured": true,
+   "extended": false,
    "exports": [
      {
        "export-name": "",
@@ -165,6 +166,11 @@ Test if the NBD URI connection is using TLS.
 Test if server can respond with structured replies (a prerequisite
 for supporting block status commands).

+=item nbdinfo --can extended-headers URI
+
+Test if server supports extended headers (a prerequisite for
+supporting 64-bit commands; implies structured replies as well).
+
 =item nbdinfo --is rotational URI

 Test if the server export is backed by something which behaves like a
@@ -312,6 +318,8 @@ Display brief command line help and exit.

 =item B<--can df>

+=item B<--can extended-headers>
+
 =item B<--can fast-zero>

 =item B<--can flush>
@@ -341,7 +349,8 @@ and the following libnbd functions: L<nbd_can_cache(3)>,
 L<nbd_can_df(3)>, L<nbd_can_fast_zero(3)>, L<nbd_can_flush(3)>,
 L<nbd_can_fua(3)>, L<nbd_can_multi_conn(3)>, L<nbd_can_trim(3)>,
 L<nbd_can_zero(3)>, L<nbd_is_read_only(3)>,
-L<nbd_get_structured_replies_negotiated(3)>.
+L<nbd_get_structured_replies_negotiated(3)>,
+L<nbd_get_extended_headers_negotiated(3)>.

 =item B<--color>

diff --git a/info/can.c b/info/can.c
index 08d6bcd5..f602ffce 100644
--- a/info/can.c
+++ b/info/can.c
@@ -50,6 +50,15 @@ do_can (void)
            strcasecmp (can, "structured_replies") == 0)
     feature = nbd_get_structured_replies_negotiated (nbd);

+  else if (strcasecmp (can, "eh") == 0 ||
+           strcasecmp (can, "extended header") == 0 ||
+           strcasecmp (can, "extended-header") == 0 ||
+           strcasecmp (can, "extended_header") == 0 ||
+           strcasecmp (can, "extended headers") == 0 ||
+           strcasecmp (can, "extended-headers") == 0 ||
+           strcasecmp (can, "extended_headers") == 0)
+    feature = nbd_get_extended_headers_negotiated (nbd);
+
   else if (strcasecmp (can, "readonly") == 0 ||
            strcasecmp (can, "read-only") == 0 ||
            strcasecmp (can, "read_only") == 0)
diff --git a/info/info-can.sh b/info/info-can.sh
index 3edc3948..e5f6a44b 100755
--- a/info/info-can.sh
+++ b/info/info-can.sh
@@ -61,6 +61,33 @@ esac
 EOF
 test $st = 2

+# --can extended-headers cannot be positively tested until nbdkit gains
+# --no-eh support.  Otherwise, it is similar to --can structured-reply.
+
+no_eh=
+if nbdkit --no-eh --help >/dev/null 2>/dev/null; then
+    no_eh=--no-eh
+    nbdkit -v -U - sh - \
+           --run '$VG nbdinfo --can extended-headers "nbd+unix:///?socket=$unixsocket"' <<'EOF'
+case "$1" in
+  get_size) echo 1024 ;;
+  pread) ;;
+  *) exit 2 ;;
+esac
+EOF
+fi
+
+st=0
+nbdkit -v -U - $no_eh sh - \
+       --run '$VG nbdinfo --can extended-headers "nbd+unix:///?socket=$unixsocket"' <<'EOF' || st=$?
+case "$1" in
+  get_size) echo 1024 ;;
+  pread) ;;
+  *) exit 2 ;;
+esac
+EOF
+test $st = 2
+
 # --can cache and --can fua require special handling because in
 # nbdkit-sh-plugin we must print "native" or "none".  Also the can_fua
 # flag is only sent if the export is writable (hence can_write below).
diff --git a/info/info-packets.sh b/info/info-packets.sh
index 82bb526c..a6b307a0 100755
--- a/info/info-packets.sh
+++ b/info/info-packets.sh
@@ -27,12 +27,27 @@ requires nbdkit --no-sr memory --version
 out=info-packets.out
 cleanup_fn rm -f $out

+# Older nbdkit does not support extended headers; --no-eh is a reliable
+# witness of whether nbdkit is new enough.
+
+no_eh=
+if nbdkit --no-eh --help >/dev/null 2>/dev/null; then
+    no_eh=--no-eh
+fi
+
 nbdkit --no-sr -U - memory size=1M \
        --run '$VG nbdinfo "nbd+unix:///?socket=$unixsocket"' > $out
 cat $out
 grep "protocol: .*using simple packets" $out

-nbdkit -U - memory size=1M \
+nbdkit $no_eh -U - memory size=1M \
        --run '$VG nbdinfo "nbd+unix:///?socket=$unixsocket"' > $out
 cat $out
 grep "protocol: .*using structured packets" $out
+
+if test x != "x$no_eh"; then
+    nbdkit -U - memory size=1M \
+           --run '$VG nbdinfo "nbd+unix:///?socket=$unixsocket"' > $out
+    cat $out
+    grep "protocol: .*using extended packets" $out
+fi
diff --git a/info/main.c b/info/main.c
index 5cd91fe1..9794c109 100644
--- a/info/main.c
+++ b/info/main.c
@@ -302,11 +302,13 @@ main (int argc, char *argv[])
     const char *protocol;
     int tls_negotiated;
     int sr_negotiated;
+    int eh_negotiated;

     /* Print per-connection fields. */
     protocol = nbd_get_protocol (nbd);
     tls_negotiated = nbd_get_tls_negotiated (nbd);
     sr_negotiated = nbd_get_structured_replies_negotiated (nbd);
+    eh_negotiated = nbd_get_extended_headers_negotiated (nbd);

     if (!json_output) {
       if (protocol) {
@@ -314,8 +316,9 @@ main (int argc, char *argv[])
         fprintf (fp, "protocol: %s", protocol);
         if (tls_negotiated >= 0)
           fprintf (fp, " %s TLS", tls_negotiated ? "with" : "without");
-        if (sr_negotiated >= 0)
+        if (eh_negotiated >= 0 && sr_negotiated >= 0)
           fprintf (fp, ", using %s packets",
+                   eh_negotiated ? "extended" :
                    sr_negotiated ? "structured" : "simple");
         fprintf (fp, "\n");
         ansi_restore (fp);
@@ -333,6 +336,8 @@ main (int argc, char *argv[])
         fprintf (fp, "\"TLS\": %s,\n", tls_negotiated ? "true" : "false");
       if (sr_negotiated >= 0)
         fprintf (fp, "\"structured\": %s,\n", sr_negotiated ? "true" : "false");
+      if (eh_negotiated >= 0)
+        fprintf (fp, "\"extended\": %s,\n", eh_negotiated ? "true" : "false");
     }

     if (!list_all)
