diff --git a/package/mac80211/patches/571-ath9k_fix_adhoc_nexttbtt.patch b/package/mac80211/patches/571-ath9k_fix_adhoc_nexttbtt.patch
new file mode 100644
index 0000000000..544c7a9c9f
--- /dev/null
+++ b/package/mac80211/patches/571-ath9k_fix_adhoc_nexttbtt.patch
@@ -0,0 +1,11 @@
+--- a/drivers/net/wireless/ath/ath9k/beacon.c
++++ b/drivers/net/wireless/ath/ath9k/beacon.c
+@@ -654,7 +654,7 @@ static void ath_beacon_config_adhoc(stru
+ 			delta = (tsf - sc->beacon.bc_tstamp);
+ 		else
+ 			delta = (tsf + 1 + (~0U - sc->beacon.bc_tstamp));
+-		nexttbtt = tsf + roundup(delta, intval);
++		nexttbtt = tsf + intval - (delta % intval);
+ 	}
+ 
+ 	ath_dbg(common, ATH_DBG_BEACON,