diff --git a/docs/changes.txt b/docs/changes.txt
index ff655f1..5944d8a 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -194,3 +194,4 @@ v0.8.1
 
 * winws2, blockcheck2: allow multiple instances in windows, linux, freebsd (not openbsd)
 * nfqws2: fix critical bug - wrong ipv6 dissection
+* zapret-auto: fix standard_failure_detector http redirect regression
diff --git a/lua/zapret-auto.lua b/lua/zapret-auto.lua
index 3050d1d..1738ad0 100644
--- a/lua/zapret-auto.lua
+++ b/lua/zapret-auto.lua
@@ -181,13 +181,16 @@ function standard_failure_detector(desync, crec)
 				end
 			elseif not arg.no_http_redirect and desync.l7payload=="http_reply" and desync.track.hostname then
 				local hdis = http_dissect_reply(desync.dis.payload)
-				if hdis and (hdis.code==302 or hdis.code==307) and hdis.headers.location and hdis.headers.location then
-					trigger = is_dpi_redirect(desync.track.hostname, hdis.headers.location.value)
-					if b_debug then
-						if trigger then
-							DLOG("standard_failure_detector: http redirect "..hdis.code.." to '"..hdis.headers.location.value.."'. looks like DPI redirect.")
-						else
-							DLOG("standard_failure_detector: http redirect "..hdis.code.." to '"..hdis.headers.location.value.."'. NOT a DPI redirect.")
+				if hdis and (hdis.code==302 or hdis.code==307) then
+					local idx_loc = array_field_search(hdis.headers, "header_low", "location")
+					if idx_loc then
+						trigger = is_dpi_redirect(desync.track.hostname, hdis.headers[idx_loc].value)
+						if b_debug then
+							if trigger then
+								DLOG("standard_failure_detector: http redirect "..hdis.code.." to '"..hdis.headers[idx_loc].value.."'. looks like DPI redirect.")
+							else
+								DLOG("standard_failure_detector: http redirect "..hdis.code.." to '"..hdis.headers[idx_loc].value.."'. NOT a DPI redirect.")
+							end
 						end
 					end
 				end
diff --git a/lua/zapret-lib.lua b/lua/zapret-lib.lua
index 927d02a..7cca4a0 100644
--- a/lua/zapret-lib.lua
+++ b/lua/zapret-lib.lua
@@ -1558,6 +1558,9 @@ function writefile(filename, data)
 	end
 	local s,err = f:write(data)
 	f:close()
+	if not s then
+		error("writefile: "..err)
+	end
 end
 
 -- DISSECTORS
diff --git a/nfq2/lua.c b/nfq2/lua.c
index 3f12aff..797f9a2 100644
--- a/nfq2/lua.c
+++ b/nfq2/lua.c
@@ -427,7 +427,7 @@ static int luacall_brandom(lua_State *L)
 {
 	lua_check_argc(L,"brandom",1);
 	lua_Integer len = luaL_checkinteger(L,1);
-
+	if (len<0) luaL_error(L, "brandom: invalid arg");
 	uint8_t *p = malloc(len);
 	if (!p) luaL_error(L, "out of memory");
 	fill_random_bytes(p,len);
@@ -440,7 +440,7 @@ static int luacall_brandom_az(lua_State *L)
 {
 	lua_check_argc(L,"brandom_az",1);
 	lua_Integer len = luaL_checkinteger(L,1);
-
+	if (len<0) luaL_error(L, "brandom_az: invalid arg");
 	uint8_t *p = malloc(len);
 	if (!p) luaL_error(L, "out of memory");
 	fill_random_az(p,len);
@@ -453,7 +453,7 @@ static int luacall_brandom_az09(lua_State *L)
 {
 	lua_check_argc(L,"brandom_az09",1);
 	lua_Integer len = luaL_checkinteger(L,1);
-
+	if (len<0) luaL_error(L, "brandom_az09: invalid arg");
 	uint8_t *p = malloc(len);
 	if (!p) luaL_error(L, "out of memory");
 	fill_random_az09(p,len);
@@ -536,6 +536,7 @@ static int luacall_bcryptorandom(lua_State *L)
 	LUA_STACK_GUARD_ENTER(L)
 
 	lua_Integer len = luaL_checkinteger(L,1);
+	if (len<0) luaL_error(L, "bcryptorandom: invalid arg");
 
 	uint8_t *p = malloc(len);
 	if (!p) luaL_error(L, "out of memory");
@@ -691,7 +692,8 @@ static int luacall_hkdf(lua_State *L)
 	const uint8_t *ikm = lua_type(L,3) == LUA_TNIL ? NULL : (uint8_t*)luaL_checklstring(L,3,&ikm_len);
 	size_t info_len=0;
 	const uint8_t *info = lua_type(L,4) == LUA_TNIL ? NULL : (uint8_t*)luaL_checklstring(L,4,&info_len);
-	size_t okm_len = (size_t)luaL_checkinteger(L,5);
+	lua_Integer okm_len = luaL_checkinteger(L,5);
+	if (okm_len<0) luaL_error(L, "hkdf: invalid arg");
 
 	uint8_t *okm = malloc(okm_len);
 	if (!okm) luaL_error(L, "out of memory");
@@ -2411,6 +2413,7 @@ static void lua_rawsend_extract_options(lua_State *L, int idx, int *repeats, uin
 		{
 			lua_getfield(L,idx,"repeats");
 			*repeats=(int)lua_tointeger(L,-1);
+			if (*repeats<0) luaL_error(L, "rawsend: negative repeats");
 			if (!*repeats) *repeats=1;
 			lua_pop(L,1);
 		}