Index: head/sys/dev/sfxge/common/ef10_rx.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_rx.c
+++ head/sys/dev/sfxge/common/ef10_rx.c
@@ -588,6 +588,9 @@
 {
 	efx_rc_t rc;
 
+	EFX_STATIC_ASSERT(EFX_RSS_KEY_SIZE ==
+	    MC_CMD_RSS_CONTEXT_SET_KEY_IN_TOEPLITZ_KEY_LEN);
+
 	if (rss_context == EFX_RSS_CONTEXT_DEFAULT) {
 		if (enp->en_rss_context_type == EFX_RX_SCALE_UNAVAILABLE) {
 			rc = ENOTSUP;
Index: head/sys/dev/sfxge/common/efx.h
===================================================================
--- head/sys/dev/sfxge/common/efx.h
+++ head/sys/dev/sfxge/common/efx.h
@@ -1912,6 +1912,7 @@
 	EFX_RX_HASH_AVAILABLE		/* Insert hash with/without RSS */
 } efx_rx_hash_support_t;
 
+#define	EFX_RSS_KEY_SIZE	40	/* RSS key size (bytes) */
 #define	EFX_RSS_TBL_SIZE	128	/* Rows in RX indirection table */
 #define	EFX_MAXRSS		64	/* RX indirection entry range */
 #define	EFX_MAXRSS_LEGACY	16	/* See bug16611 and bug17213 */