Index: libsmb/smb_signing.c
===================================================================
--- libsmb/smb_signing.c	(revision 17428)
+++ libsmb/smb_signing.c	(working copy)
@@ -847,6 +847,9 @@
 
 	while (get_sequence_for_reply(&data->outstanding_packet_list, mid, &dummy_seq))
 		;
+
+	/* cancel doesn't send a reply so doesn't burn a sequence number. */
+	data->send_seq_num -= 1;
 }
 
 /***********************************************************