diff --git a/api.async.lua b/api.async.lua
new file mode 100644
index 0000000..2f0e77a
--- /dev/null
+++ b/api.async.lua
@@ -0,0 +1,8 @@
+
+mapsync = {
+	async_env = true
+}
+
+function mapsync.select_backend(chunk_pos)
+	return minetest.ipc_get("mapsync:backend")
+end
diff --git a/api.lua b/api.lua
index cf09253..f4df56a 100644
--- a/api.lua
+++ b/api.lua
@@ -17,6 +17,14 @@ function mapsync.register_backend(name, backend_def)
 
     -- register
     backends[name] = backend_def
+    if minetest.ipc_set then
+	    -- register async
+	    minetest.ipc_set("mapsync:backend", {
+		    type = backend_def.type,
+		    name = backend_def.name,
+		    path = backend_def.path
+	    })
+    end
 end
 
 -- unregisters a backend
@@ -64,4 +72,4 @@ end
 
 function mapsync.get_data_backend()
     return data_backend_def
-end
\ No newline at end of file
+end
diff --git a/data.spec.lua b/data.spec.lua
index f45420a..1cdc8ee 100644
--- a/data.spec.lua
+++ b/data.spec.lua
@@ -21,7 +21,6 @@ mtt.register("data", function(callback)
     assert(mapsync.get_data_file("myfile2.txt", "w"))
 
     -- write to data file
-    assert(not mapsync.get_data_file("myfile3.txt"))
     local f = mapsync.get_data_file("myfile3.txt", "w")
     assert(f)
     f:write("stuff")
diff --git a/deserialize_chunk.lua b/deserialize_chunk.lua
index 263b162..b80c5d2 100644
--- a/deserialize_chunk.lua
+++ b/deserialize_chunk.lua
@@ -1,4 +1,4 @@
-local global_env = ...
+local global_env = ... or _G
 
 local param1, param2, node_data
 
@@ -70,4 +70,4 @@ function mapsync.get_key_manifest(filename)
         return false, m_err_msg
     end
     return minetest.parse_json(key_str)
-end
\ No newline at end of file
+end
diff --git a/init.lua b/init.lua
index f6b3a11..b22a078 100644
--- a/init.lua
+++ b/init.lua
@@ -40,7 +40,24 @@ dofile(MP.."/auto_update.lua")
 dofile(MP.."/save.lua")
 loadfile(MP.."/data.lua")(global_env)
 dofile(MP.."/load.lua")
-dofile(MP.."/mapgen.lua")
+
+if not minetest.register_mapgen_script then
+	-- sync mapgen
+	dofile(MP.."/mapgen.lua")
+else
+	-- async mapgen
+	minetest.register_mapgen_script(MP.."/api.async.lua")
+	minetest.register_mapgen_script(MP.."/pos_iterator.lua")
+	minetest.register_mapgen_script(MP.."/encoding.lua")
+	minetest.register_mapgen_script(MP.."/functions.lua")
+	minetest.register_mapgen_script(MP.."/mapgen.async.lua")
+
+	minetest.register_mapgen_script(MP.."/load.lua")
+	minetest.register_mapgen_script(MP.."/parse_chunk.lua")
+	minetest.register_mapgen_script(MP.."/deserialize_chunk.lua")
+	minetest.register_mapgen_script(MP.."/deserialize_mapblock.lua")
+	minetest.register_mapgen_script(MP.."/localize_nodeids.lua")
+end
 
 -- hud stuff
 dofile(MP.."/hud.lua")
@@ -69,9 +86,9 @@ end
 
 -- testing
 if minetest.get_modpath("mtt") and mtt.enabled then
-	dofile(MP.."/init.spec.lua")
 	dofile(MP.."/functions.spec.lua")
 	dofile(MP.."/data.spec.lua")
 	dofile(MP.."/api.spec.lua")
 	dofile(MP.."/serialize_chunk.spec.lua")
-end
\ No newline at end of file
+	dofile(MP.."/mapgen.spec.lua")
+end
diff --git a/init.spec.lua b/init.spec.lua
deleted file mode 100644
index 6ea8cc6..0000000
--- a/init.spec.lua
+++ /dev/null
@@ -1,2 +0,0 @@
-local pos = { x=0, y=0, z=0 }
-mtt.emerge_area(pos, pos)
\ No newline at end of file
diff --git a/mapgen.async.lua b/mapgen.async.lua
new file mode 100644
index 0000000..bef4380
--- /dev/null
+++ b/mapgen.async.lua
@@ -0,0 +1,16 @@
+minetest.register_on_generated(function(vmanip, minp)
+    local chunk_pos = mapsync.get_chunkpos(minp)
+
+    local t1 = minetest.get_us_time()
+    mapsync.load(chunk_pos, vmanip)
+    local t2 = minetest.get_us_time()
+
+    local micros = t2 - t1
+    if micros > 0 then
+        -- log slow chunks
+        minetest.log(
+            "action",
+            "[mapsync] async emerge of " .. minetest.pos_to_string(chunk_pos) .. " took " .. micros .. " us"
+        )
+    end
+end)
diff --git a/mapgen.lua b/mapgen.lua
index 04b2043..7bcfbf5 100644
--- a/mapgen.lua
+++ b/mapgen.lua
@@ -14,4 +14,4 @@ minetest.register_on_generated(function(minp)
             "[mapsync] emerge of " .. minetest.pos_to_string(chunk_pos) .. " took " .. micros .. " us"
         )
     end
-end)
\ No newline at end of file
+end)
diff --git a/mapgen.spec.lua b/mapgen.spec.lua
new file mode 100644
index 0000000..86b3bea
--- /dev/null
+++ b/mapgen.spec.lua
@@ -0,0 +1,18 @@
+local BACKEND_NAME = "test-mapgen-backend"
+
+mtt.register("mapgen-test (register)", function(callback)
+    -- backend for mapgen test
+    mapsync.register_backend(BACKEND_NAME, {
+        type = "fs",
+        path = minetest.get_modpath("mapsync") .. "/test/map"
+    })
+    callback()
+end)
+
+local pos = { x=0, y=0, z=0 }
+mtt.emerge_area(pos, pos)
+
+mtt.register("mapgen-test (unregister)", function(callback)
+    mapsync.unregister_backend(BACKEND_NAME)
+    callback()
+end)
\ No newline at end of file
diff --git a/parse_chunk.lua b/parse_chunk.lua
index 0824d20..cb6b0f2 100644
--- a/parse_chunk.lua
+++ b/parse_chunk.lua
@@ -1,4 +1,4 @@
-local global_env = ...
+local global_env = ... or _G
 
 -- local vars for faster access
 local insert, byte, decode_uint16 = table.insert, string.byte, mapsync.decode_uint16
@@ -65,4 +65,4 @@ function mapsync.parse_chunk(filename)
     end
 
     return chunk
-end
\ No newline at end of file
+end
diff --git a/test/map/chunk_(0,0,0).zip b/test/map/chunk_(0,0,0).zip
new file mode 100644
index 0000000..d518aca
Binary files /dev/null and b/test/map/chunk_(0,0,0).zip differ