diff --git a/bot/world/chunk.go b/bot/world/chunk.go
index 9e71d3e..43cfa8b 100644
--- a/bot/world/chunk.go
+++ b/bot/world/chunk.go
@@ -112,7 +112,7 @@ func (d *directSection) SetBlock(x, y, z int, s BlockStatus) {
 	padding := offset % 64
 	const maxUint64 = 1<<64 - 1
 	mask := uint64(maxUint64<<(padding+d.bpb) | (1<<padding - 1))
-	d.data[offset/64] = uint64(d.data[offset/64])&mask | uint64(s)<<padding
+	d.data[offset/64] = d.data[offset/64]&mask | uint64(s)<<padding
 	if padding > 64-d.bpb {
 		l := padding - (64 - d.bpb)
 		d.data[offset/64+1] = d.data[offset/64+1]&(maxUint64<<l) | uint64(s)>>(64-padding)
diff --git a/bot/world/chunk_test.go b/bot/world/chunk_test.go
new file mode 100644
index 0000000..2878501
--- /dev/null
+++ b/bot/world/chunk_test.go
@@ -0,0 +1,48 @@
+package world
+
+import (
+	"github.com/Tnze/go-mc/data"
+	"math/rand"
+	"testing"
+)
+
+func newDirectSection(bpb int) *directSection {
+	return &directSection{
+		bpb:  bpb,
+		data: make([]uint64, 16*16*16*bpb/64),
+	}
+}
+
+func TestDirectSection(t *testing.T) {
+	for bpb := 3; bpb <= data.BitsPerBlock; bpb++ {
+		s := newDirectSection(bpb)
+		for _, dataset := range [][16 * 16 * 16]BlockStatus{secData(bpb), randData(bpb)} {
+			for i := 0; i < 16*16*16; i++ {
+				s.SetBlock(i%16, i/16%16, i/16/16, dataset[i])
+			}
+			for i := 0; i < 16*16*16; i++ {
+				if s := s.GetBlock(i%16, i/16%16, i/16/16); dataset[i] != s {
+					t.Fatalf("direct section error: want: %v, get %v", dataset[i], s)
+				}
+			}
+		}
+	}
+}
+
+func secData(bpb int) (data [16 * 16 * 16]BlockStatus) {
+	mask := 1<<bpb - 1
+	var v int
+	for i := range data {
+		data[i] = BlockStatus(v)
+		v = (v + 1) & mask
+	}
+	return
+}
+
+func randData(bpb int) (data [16 * 16 * 16]BlockStatus) {
+	data = secData(bpb)
+	rand.Shuffle(len(data), func(i, j int) {
+		data[i], data[j] = data[j], data[i]
+	})
+	return
+}