diff --git a/common/buf/multi_buffer.go b/common/buf/multi_buffer.go
index 91b9a247..b65a1471 100644
--- a/common/buf/multi_buffer.go
+++ b/common/buf/multi_buffer.go
@@ -141,16 +141,17 @@ func SplitSize(mb MultiBuffer, size int32) (MultiBuffer, MultiBuffer) {
 
 	totalBytes := int32(0)
 	var r MultiBuffer
-	endIndex := 0
+	endIndex := -1
 	for i := range mb {
 		if totalBytes+mb[i].Len() > size {
 			endIndex = i
 			break
 		}
+		totalBytes += mb[i].Len()
 		r = append(r, mb[i])
 		mb[i] = nil
 	}
-	if endIndex == len(mb) {
+	if endIndex == -1 {
 		// To reuse mb array
 		mb = mb[:0]
 	} else {
diff --git a/common/buf/multi_buffer_test.go b/common/buf/multi_buffer_test.go
index 1e412522..8fd20d4d 100644
--- a/common/buf/multi_buffer_test.go
+++ b/common/buf/multi_buffer_test.go
@@ -5,6 +5,8 @@ import (
 	"io"
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
+
 	"v2ray.com/core/common"
 	. "v2ray.com/core/common/buf"
 	. "v2ray.com/ext/assert"
@@ -37,13 +39,58 @@ func TestMultiBufferAppend(t *testing.T) {
 }
 
 func TestMultiBufferSliceBySizeLarge(t *testing.T) {
-	assert := With(t)
-
 	lb := make([]byte, 8*1024)
 	common.Must2(io.ReadFull(rand.Reader, lb))
 
 	mb := MergeBytes(nil, lb)
 
 	mb, mb2 := SplitSize(mb, 1024)
-	assert(mb2.Len(), Equals, int32(1024))
+	if mb2.Len() != 1024 {
+		t.Error("expect length 1024, but got ", mb2.Len())
+	}
+	if mb.Len() != 7*1024 {
+		t.Error("expect length 7*1024, but got ", mb.Len())
+	}
+
+	mb, mb3 := SplitSize(mb, 7*1024)
+	if mb3.Len() != 7*1024 {
+		t.Error("expect length 7*1024, but got", mb.Len())
+	}
+
+	if !mb.IsEmpty() {
+		t.Error("expect empty buffer, but got ", mb.Len())
+	}
+}
+
+func TestMultiBufferSplitFirst(t *testing.T) {
+	b1 := New()
+	b1.WriteString("b1")
+
+	b2 := New()
+	b2.WriteString("b2")
+
+	b3 := New()
+	b3.WriteString("b3")
+
+	var mb MultiBuffer
+	mb = append(mb, b1, b2, b3)
+
+	mb, c1 := SplitFirst(mb)
+	if diff := cmp.Diff(b1.String(), c1.String()); diff != "" {
+		t.Error(diff)
+	}
+
+	mb, c2 := SplitFirst(mb)
+	if diff := cmp.Diff(b2.String(), c2.String()); diff != "" {
+		t.Error(diff)
+	}
+
+	mb, c3 := SplitFirst(mb)
+	if diff := cmp.Diff(b3.String(), c3.String()); diff != "" {
+		t.Error(diff)
+	}
+
+	if !mb.IsEmpty() {
+		t.Error("expect empty buffer, but got ", mb.String())
+	}
 }