diff --git a/sys/dev/ixgbe/ix_txrx.c b/sys/dev/ixgbe/ix_txrx.c
index 63a29d69d5f9..45690b2afcf7 100644
--- a/sys/dev/ixgbe/ix_txrx.c
+++ b/sys/dev/ixgbe/ix_txrx.c
@@ -297,6 +297,8 @@ ixgbe_isc_txd_credits_update(void *arg, uint16_t txqid, bool clear)
 	ntxd = scctx->isc_ntxd[0];
 	do {
 		delta = (int32_t)cur - (int32_t)prev;
+		if (prev == 0 && cur == 0)
+			delta += 1;
 		if (delta < 0)
 			delta += ntxd;
 
diff --git a/sys/dev/ixl/ixl_txrx.c b/sys/dev/ixl/ixl_txrx.c
index ec14ab14ee8f..ea215f272d9f 100644
--- a/sys/dev/ixl/ixl_txrx.c
+++ b/sys/dev/ixl/ixl_txrx.c
@@ -516,7 +516,13 @@ ixl_isc_txd_credits_update_dwb(void *arg, uint16_t txqid, bool clear)
 	ntxd = scctx->isc_ntxd[0];
 	do {
 		delta = (int32_t)cur - (int32_t)prev;
+		/*
+		 * XXX This appears to be a hack for first-packet.
+		 * A correct fix would prevent prev == cur in the first place.
+		 */
 		MPASS(prev == 0 || delta != 0);
+		if (prev == 0 && cur == 0)
+			delta += 1;
 		if (delta < 0)
 			delta += ntxd;
 #if 0