diff --git a/mods/dungeon_loot/mapgen.lua b/mods/dungeon_loot/mapgen.lua
index 3b597f2efb..2bca1f3229 100644
--- a/mods/dungeon_loot/mapgen.lua
+++ b/mods/dungeon_loot/mapgen.lua
@@ -14,62 +14,6 @@ local function random_sample(rand, list, count)
 	return ret
 end
 
-local function find_walls(cpos, is_temple)
-	local is_wall = function(node)
-		return node.name ~= "air" and node.name ~= "ignore"
-	end
-
-	local dirs = {{x=1, z=0}, {x=-1, z=0}, {x=0, z=1}, {x=0, z=-1}}
-	local get_node = minetest.get_node
-
-	local ret = {}
-	local mindist = {x=0, z=0}
-	local min = function(a, b) return a ~= 0 and math.min(a, b) or b end
-	for _, dir in ipairs(dirs) do
-		for i = 1, 9 do -- 9 = max room size / 2
-			local pos = vector.add(cpos, {x=dir.x*i, y=0, z=dir.z*i})
-
-			-- continue in that direction until we find a wall-like node
-			local node = get_node(pos)
-			if is_wall(node) then
-				local front_below = vector.subtract(pos, {x=dir.x, y=1, z=dir.z})
-				local above = vector.add(pos, {x=0, y=1, z=0})
-
-				-- check that it:
-				--- is at least 2 nodes high (not a staircase)
-				--- has a floor
-				if is_wall(get_node(front_below)) and is_wall(get_node(above)) then
-					table.insert(ret, {pos = pos, facing = {x=-dir.x, y=0, z=-dir.z}})
-					if dir.z == 0 then
-						mindist.x = min(mindist.x, i-1)
-					else
-						mindist.z = min(mindist.z, i-1)
-					end
-				end
-				-- abort even if it wasn't a wall cause something is in the way
-				break
-			end
-		end
-	end
-
-	local biome = minetest.get_biome_data(cpos)
-	biome = biome and minetest.get_biome_name(biome.biome) or ""
-	local type = "normal"
-	if is_temple or biome:find("desert") == 1 then
-		type = "desert"
-	elseif biome:find("sandstone_desert") == 1 then
-		type = "sandstone"
-	elseif biome:find("icesheet") == 1 then
-		type = "ice"
-	end
-
-	return {
-		walls = ret,
-		size = {x=mindist.x*2, z=mindist.z*2},
-		type = type,
-	}
-end
-
 local function populate_chest(pos, rand, dungeontype)
 	--minetest.chat_send_all("chest placed at " .. minetest.pos_to_string(pos) .. " [" .. dungeontype .. "]")
 	--minetest.add_node(vector.add(pos, {x=0, y=1, z=0}), {name="default:torch", param2=1})
@@ -121,30 +65,13 @@ local function populate_chest(pos, rand, dungeontype)
 	end
 end
 
-
-minetest.register_on_generated(function(minp, maxp, blockseed)
-	local gennotify = minetest.get_mapgen_object("gennotify")
-	local poslist = gennotify["dungeon"] or {}
-	local n_dungeons = #poslist
-	-- Add MGv6 desert temples to the list too
-	for _, entry in ipairs(gennotify["temple"] or {}) do
-		table.insert(poslist, entry)
+local function place_chests(candidates, blockseed)
+	if #candidates == 0 then
+		return
 	end
-	if #poslist == 0 then return end
 
 	local noise = minetest.get_perlin(10115, 4, 0.5, 1)
-	local rand = PcgRandom(noise3d_integer(noise, poslist[1]))
-
-	local candidates = {}
-	-- process at most 8 rooms to keep runtime of this predictable
-	local num_process = math.min(#poslist, 8)
-	for i = 1, num_process do
-		local room = find_walls(poslist[i], i > n_dungeons)
-		-- skip small rooms and everything that doesn't at least have 3 walls
-		if math.min(room.size.x, room.size.z) >= 4 and #room.walls >= 3 then
-			table.insert(candidates, room)
-		end
-	end
+	local rand = PcgRandom(blockseed)
 
 	local num_chests = rand:next(dungeon_loot.CHESTS_MIN, dungeon_loot.CHESTS_MAX)
 	num_chests = math.min(#candidates, num_chests)
@@ -170,4 +97,24 @@ minetest.register_on_generated(function(minp, maxp, blockseed)
 			populate_chest(chestpos, PcgRandom(noise3d_integer(noise, chestpos)), room.type)
 		end
 	end
-end)
+end
+
+if minetest.register_mapgen_script then
+	-- dungeon rooms are scanned in mapgen thread
+	minetest.set_gen_notify({custom=true}, nil, {"dungeon_loot:candidates"})
+	minetest.register_mapgen_script(minetest.get_modpath("dungeon_loot") .. "/scan.lua")
+	minetest.register_on_generated(function(minp, maxp, blockseed)
+		local gennotify = minetest.get_mapgen_object("gennotify")
+		local candidates = gennotify.custom["dungeon_loot:candidates"]
+		assert(type(candidates) == "table", "candidates must exist")
+		place_chests(candidates, blockseed)
+	end)
+else
+	-- dungeon rooms are scanned in callback here
+	dofile(minetest.get_modpath("dungeon_loot") .. "/scan.lua")
+	minetest.register_on_generated(function(minp, maxp, blockseed)
+		-- process at most 8 rooms to keep runtime of this predictable
+		local candidates = dungeon_loot._internal_find_rooms(8)
+		place_chests(candidates, blockseed)
+	end)
+end
diff --git a/mods/dungeon_loot/scan.lua b/mods/dungeon_loot/scan.lua
new file mode 100644
index 0000000000..f01e7ba565
--- /dev/null
+++ b/mods/dungeon_loot/scan.lua
@@ -0,0 +1,92 @@
+if minetest.save_gen_notify then
+	dungeon_loot = {}
+end
+
+local function find_walls(cpos, is_temple)
+	local is_wall = function(node)
+		return node.name ~= "air" and node.name ~= "ignore"
+	end
+
+	local dirs = {{x=1, z=0}, {x=-1, z=0}, {x=0, z=1}, {x=0, z=-1}}
+	local get_node = minetest.get_node
+
+	local ret = {}
+	local mindist = {x=0, z=0}
+	local min = function(a, b) return a ~= 0 and math.min(a, b) or b end
+	for _, dir in ipairs(dirs) do
+		for i = 1, 9 do -- 9 = max room size / 2
+			local pos = vector.add(cpos, {x=dir.x*i, y=0, z=dir.z*i})
+
+			-- continue in that direction until we find a wall-like node
+			local node = get_node(pos)
+			if is_wall(node) then
+				local front_below = vector.subtract(pos, {x=dir.x, y=1, z=dir.z})
+				local above = vector.add(pos, {x=0, y=1, z=0})
+
+				-- check that it:
+				--- is at least 2 nodes high (not a staircase)
+				--- has a floor
+				if is_wall(get_node(front_below)) and is_wall(get_node(above)) then
+					table.insert(ret, {pos = pos, facing = {x=-dir.x, y=0, z=-dir.z}})
+					if dir.z == 0 then
+						mindist.x = min(mindist.x, i-1)
+					else
+						mindist.z = min(mindist.z, i-1)
+					end
+				end
+				-- abort even if it wasn't a wall cause something is in the way
+				break
+			end
+		end
+	end
+
+	local biome = minetest.get_biome_data(cpos)
+	biome = biome and minetest.get_biome_name(biome.biome) or ""
+	local type = "normal"
+	if is_temple or biome:find("desert") == 1 then
+		type = "desert"
+	elseif biome:find("sandstone_desert") == 1 then
+		type = "sandstone"
+	elseif biome:find("icesheet") == 1 then
+		type = "ice"
+	end
+
+	return {
+		walls = ret,
+		size = {x=mindist.x*2, z=mindist.z*2},
+		type = type,
+	}
+end
+
+function dungeon_loot._internal_find_rooms(max_rooms)
+	local gennotify = minetest.get_mapgen_object("gennotify")
+	local poslist = gennotify["dungeon"] or {}
+	local n_dungeons = #poslist
+	-- Add MGv6 desert temples to the list too
+	for _, entry in ipairs(gennotify["temple"] or {}) do
+		table.insert(poslist, entry)
+	end
+	if #poslist == 0 then
+		return {}
+	end
+
+	local candidates = {}
+	local num_process = math.min(#poslist, max_rooms)
+	for i = 1, num_process do
+		local room = find_walls(poslist[i], i > n_dungeons)
+		-- skip small rooms and everything that doesn't at least have 3 walls
+		if math.min(room.size.x, room.size.z) >= 4 and #room.walls >= 3 then
+			table.insert(candidates, room)
+		end
+	end
+
+	return candidates
+end
+
+-- if loaded inside mapgen env, do our job there and export the result
+if minetest.save_gen_notify then
+	minetest.register_on_generated(function(vmanip, minp, maxp, blockseed)
+		local candidates = dungeon_loot._internal_find_rooms(9999)
+		minetest.save_gen_notify("dungeon_loot:candidates", candidates)
+	end)
+end