diff --git a/package/mac80211/patches/560-minstrel_ht.patch b/package/mac80211/patches/560-minstrel_ht.patch
index 6c3d08eac2..2f2aa9d398 100644
--- a/package/mac80211/patches/560-minstrel_ht.patch
+++ b/package/mac80211/patches/560-minstrel_ht.patch
@@ -100,7 +100,7 @@
 +/* Transmission time for a packet containing (syms) symbols */
 +#define MCS_SYMBOL_TIME(sgi, syms)					\
 +	(sgi ?								\
-+	  ((syms) * 18 + 4) / 5 :	/* syms * 3.6 us */		\
++	  ((syms) * 18 + 4) / 6 :	/* syms * 3.6 us */		\
 +	  (syms) << 2			/* syms * 4 us */		\
 +	)
 +
diff --git a/package/mac80211/patches/580-ath9k_fix_duration_calculation.patch b/package/mac80211/patches/580-ath9k_fix_duration_calculation.patch
new file mode 100644
index 0000000000..219e4ee363
--- /dev/null
+++ b/package/mac80211/patches/580-ath9k_fix_duration_calculation.patch
@@ -0,0 +1,14 @@
+--- a/drivers/net/wireless/ath/ath9k/xmit.c
++++ b/drivers/net/wireless/ath/ath9k/xmit.c
+@@ -27,9 +27,9 @@
+ #define HT_STF                  4
+ #define HT_LTF(_ns)             (4 * (_ns))
+ #define SYMBOL_TIME(_ns)        ((_ns) << 2) /* ns * 4 us */
+-#define SYMBOL_TIME_HALFGI(_ns) (((_ns) * 18 + 4) / 5)  /* ns * 3.6 us */
++#define SYMBOL_TIME_HALFGI(_ns) (((_ns) * 18 + 4) / 6)  /* ns * 3.6 us */
+ #define NUM_SYMBOLS_PER_USEC(_usec) (_usec >> 2)
+-#define NUM_SYMBOLS_PER_USEC_HALFGI(_usec) (((_usec*5)-4)/18)
++#define NUM_SYMBOLS_PER_USEC_HALFGI(_usec) (((_usec*6)-4)/18)
+ 
+ #define OFDM_SIFS_TIME    	    16
+