diff --git a/mtt.lua b/mtt.lua
index 6a74185..c9070b0 100644
--- a/mtt.lua
+++ b/mtt.lua
@@ -18,7 +18,7 @@ mtt.register("register and export", function(callback)
 end)
 
 
-mtt.register("serlize_chunk", function(callback)
+mtt.register("serialize_chunk", function(callback)
     local pos1 = { x=0, y=0, z=0 }
     local pos2 = { x=20, y=20, z=20 }
 
diff --git a/serialize.lua b/serialize.lua
index b1190c0..54cc5a9 100644
--- a/serialize.lua
+++ b/serialize.lua
@@ -5,6 +5,10 @@ local char, encode_uint16, insert = string.char, mapsync.encode_uint16, table.in
 
 function mapsync.serialize_chunk(chunk_pos, filename)
     local f = global_env.io.open(filename, "w")
+    if not f then
+        return false, "could not open '" .. filename .. "'"
+    end
+
     local zip = mtzip.zip(f)
 
     local blockdata_list = {}