diff --git a/cmd/mcadump/mcadump.go b/cmd/mcadump/mcadump.go
index a665e48..64110f2 100644
--- a/cmd/mcadump/mcadump.go
+++ b/cmd/mcadump/mcadump.go
@@ -101,7 +101,7 @@ func pack(f, o string) {
 		checkerr(fmt.Errorf("cannot use %s as mca file name: %v", rn, err))
 	}
 
-	fn := fmt.Sprintf("r.%d.%d.mca", x/32, z/32)
+	fn := fmt.Sprintf("r.%d.%d.mca", x>>5, z>>5)
 	r, err := region.Open(fn)
 	if err != nil && os.IsNotExist(err) {
 		r, err = region.Create(filepath.Join(o, fn))
diff --git a/go.sum b/go.sum
index d2859d8..6b512af 100644
--- a/go.sum
+++ b/go.sum
@@ -4,4 +4,5 @@ github.com/mattn/go-colorable v0.1.2 h1:/bC9yWikZXAL9uJdulbSfyVNIR3n3trXl+v8+1sx
 github.com/mattn/go-colorable v0.1.2/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
 github.com/mattn/go-isatty v0.0.8 h1:HLtExJ+uU2HOZ+wI0Tt5DtUDrx8yhUqDcp7fYERX4CE=
 github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
+golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223 h1:DH4skfRX4EBpamg7iV4ZlCpblAHI6s6TDM39bFZumv8=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=