diff --git a/sys/dev/iwx/if_iwx.c b/sys/dev/iwx/if_iwx.c
--- a/sys/dev/iwx/if_iwx.c
+++ b/sys/dev/iwx/if_iwx.c
@@ -432,7 +432,7 @@
 static int	iwx_rxmq_get_signal_strength(struct iwx_softc *, struct iwx_rx_mpdu_desc *);
 static void	iwx_rx_rx_phy_cmd(struct iwx_softc *, struct iwx_rx_packet *,
     struct iwx_rx_data *);
-static int	iwx_get_noise(const struct iwx_statistics_rx_non_phy *);
+static int	iwx_get_noise(struct iwx_softc *, const struct iwx_statistics_rx_non_phy *);
 static int	iwx_rx_hwdecrypt(struct iwx_softc *, struct mbuf *, uint32_t);
 #if 0
 int	iwx_ccmp_decap(struct iwx_softc *, struct mbuf *,
@@ -4208,6 +4208,17 @@
 	return 0;
 }
 
+/*
+ * @brief Return a single signal strength for the given frame.
+ *
+ * The firmware communicates up an energy field which is the negative of
+ * the dBm value.  Ie, the number is positive and it increases as the
+ * signal level decreases.
+ *
+ * Fetch the two values, map 0 (inactive antenna) to -256 dBm which is a
+ * very small number, negate a non-zero value so it's mapped into a dBm
+ * value, then choose the maximum value to return.
+ */
 static int
 iwx_rxmq_get_signal_strength(struct iwx_softc *sc,
     struct iwx_rx_mpdu_desc *desc)
@@ -4253,12 +4264,18 @@
 }
 
 /*
- * Retrieve the average noise (in dBm) among receivers.
+ * @brief Retrieve the average noise (in dBm) among receivers.
+ *
+ * Note: This routine calculates the noise floor sum incorrectly, as
+ * you can't just linearly add the logarithm based dB units together.
+ *
+ * If no noise floor is available then this routine will return -127.
  */
 static int
-iwx_get_noise(const struct iwx_statistics_rx_non_phy *stats)
+iwx_get_noise(struct iwx_softc *sc,
+    const struct iwx_statistics_rx_non_phy *stats)
 {
-	int i, total, nbant, noise;
+	int i, total, nbant, noise, ret;
 
 	total = nbant = noise = 0;
 	for (i = 0; i < 3; i++) {
@@ -4270,7 +4287,14 @@
 	}
 
 	/* There should be at least one antenna but check anyway. */
-	return (nbant == 0) ? -127 : (total / nbant) - 107;
+	if (nbant == 0)
+		ret = -127;
+	else if (total == 0)
+		ret = -127;
+	else
+		ret = (total / nbant) - 127;
+
+	return (ret);
 }
 
 #if 0
@@ -4687,7 +4711,17 @@
 
 	/* rssi is in 1/2db units */
 	rxs.c_rssi = rssi * 2;
-	rxs.c_nf = sc->sc_noise;
+
+	/* noise floor is in 1dB units */
+	if (sc->sc_noise == -127)
+		/*
+		 * For now choose /a/ default, net80211 expects nf to be passed
+		 * in various places and older drivers fake NF values where
+		 * needed.
+		 */
+		rxs.c_nf = -107;
+	else
+		rxs.c_nf = sc->sc_noise;
 
 	if (pad) {
 		rxs.c_pktflags |= IEEE80211_RX_F_DECRYPTED;
@@ -9129,11 +9163,16 @@
 			break;
 		}
 
+		/*
+		 * TODO: is this the right struct to use? Look at what
+		 * mvm is doing for statistics notification (eg
+		 * iwl_mvm_handle_rx_statistics() .
+		 */
 		case IWX_STATISTICS_NOTIFICATION: {
 			struct iwx_notif_statistics *stats;
 			SYNC_RESP_STRUCT(stats, pkt);
 			memcpy(&sc->sc_stats, stats, sizeof(sc->sc_stats));
-			sc->sc_noise = iwx_get_noise(&stats->rx.general);
+			sc->sc_noise = iwx_get_noise(sc, &stats->rx.general);
 			break;
 		}