diff --git a/decor.lua b/decor.lua
index 7596a8b..9563e49 100644
--- a/decor.lua
+++ b/decor.lua
@@ -757,34 +757,9 @@ if minetest.registered_nodes["default:coral_green"] then
 end
 
 
-local random = math.random
-
--- Generate Illumishroom in caves on top of coal
-minetest.register_on_generated(function(minp, maxp)
-
-	if minp.y > -30 or maxp.y < -3000 then
-		return
-	end
-
-	local bpos
-	local coal = minetest.find_nodes_in_area_under_air(
-			minp, maxp, "default:stone_with_coal")
-
-	for n = 1, #coal do
-
-		if random(2) == 1 then
-
-			bpos = {x = coal[n].x, y = coal[n].y + 1, z = coal[n].z}
-
-			if bpos.y > -3000 and bpos.y < -2000 then
-				minetest.swap_node(bpos, {name = "ethereal:illumishroom3"})
-
-			elseif bpos.y > -2000 and bpos.y < -1000 then
-				minetest.swap_node(bpos, {name = "ethereal:illumishroom2"})
-
-			elseif bpos.y > -1000 and bpos.y < -30 then
-				minetest.swap_node(bpos, {name = "ethereal:illumishroom"})
-			end
-		end
-	end
-end)
+-- register async mapgen script
+if minetest.register_mapgen_script then
+	minetest.register_mapgen_script(minetest.get_modpath("ethereal") .. "/decor_on_generated.lua")
+else
+	dofile(minetest.get_modpath("ethereal") .. "/decor_on_generated.lua")
+end
diff --git a/decor_on_generated.lua b/decor_on_generated.lua
new file mode 100644
index 0000000..455aa9e
--- /dev/null
+++ b/decor_on_generated.lua
@@ -0,0 +1,39 @@
+
+local random = math.random
+
+-- Generate Illumishroom in caves on top of coal
+local function generate(minp, maxp)
+
+	if minp.y > -30 or maxp.y < -3000 then
+		return
+	end
+
+	local coal = minetest.find_nodes_in_area_under_air(
+			minp, maxp, "default:stone_with_coal")
+
+	for n = 1, #coal do
+
+		if random(2) == 1 then
+
+			local bpos = {x = coal[n].x, y = coal[n].y + 1, z = coal[n].z}
+
+			if bpos.y > -3000 and bpos.y < -2000 then
+				minetest.set_node(bpos, {name = "ethereal:illumishroom3"})
+			elseif bpos.y > -2000 and bpos.y < -1000 then
+				minetest.set_node(bpos, {name = "ethereal:illumishroom2"})
+			elseif bpos.y > -1000 and bpos.y < -30 then
+				minetest.set_node(bpos, {name = "ethereal:illumishroom"})
+			end
+		end
+	end
+end
+
+if minetest.save_gen_notify then -- async env (5.9+)
+	minetest.register_on_generated(function(vmanip, minp, maxp, blockseed)
+		generate(minp, maxp)
+	end)
+else -- main thread (5.8 and earlier)
+	minetest.register_on_generated(function(minp, maxp, blockseed)
+		generate(minp, maxp)
+	end)
+end
\ No newline at end of file