Index: head/sys/dev/sfxge/sfxge_tx.h
===================================================================
--- head/sys/dev/sfxge/sfxge_tx.h
+++ head/sys/dev/sfxge/sfxge_tx.h
@@ -53,11 +53,13 @@
  * TSO, the mbuf length may be just over 64K, divided into 2K mbuf
  * clusters taking into account that the first may be not 2K cluster
  * boundary aligned.
+ * Packet header may be split into two segments because of, for example,
+ * VLAN header insertion.
  * The chain could be longer than this initially, but can be shortened
  * with m_collapse().
  */
 #define	SFXGE_TX_MAPPING_MAX_SEG					\
-	(1 + howmany(SFXGE_TSO_MAX_SIZE, MCLBYTES) + 1)
+	(2 + howmany(SFXGE_TSO_MAX_SIZE, MCLBYTES) + 1)
 
 /*
  * Buffer mapping flags.