diff --git a/core/types/derive_sha.go b/core/types/derive_sha.go
index 51b8506bce..51a10f3f3d 100644
--- a/core/types/derive_sha.go
+++ b/core/types/derive_sha.go
@@ -17,8 +17,6 @@
 package types
 
 import (
-	"bytes"
-
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/rlp"
 )
@@ -37,26 +35,24 @@ type Hasher interface {
 
 func DeriveSha(list DerivableList, hasher Hasher) common.Hash {
 	hasher.Reset()
-	keybuf := new(bytes.Buffer)
 
 	// StackTrie requires values to be inserted in increasing
 	// hash order, which is not the order that `list` provides
 	// hashes in. This insertion sequence ensures that the
 	// order is correct.
+
+	var buf []byte
 	for i := 1; i < list.Len() && i <= 0x7f; i++ {
-		keybuf.Reset()
-		rlp.Encode(keybuf, uint(i))
-		hasher.Update(keybuf.Bytes(), list.GetRlp(i))
+		buf = rlp.AppendUint64(buf[:0], uint64(i))
+		hasher.Update(buf, list.GetRlp(i))
 	}
 	if list.Len() > 0 {
-		keybuf.Reset()
-		rlp.Encode(keybuf, uint(0))
-		hasher.Update(keybuf.Bytes(), list.GetRlp(0))
+		buf = rlp.AppendUint64(buf[:0], 0)
+		hasher.Update(buf, list.GetRlp(0))
 	}
 	for i := 0x80; i < list.Len(); i++ {
-		keybuf.Reset()
-		rlp.Encode(keybuf, uint(i))
-		hasher.Update(keybuf.Bytes(), list.GetRlp(i))
+		buf = rlp.AppendUint64(buf[:0], uint64(i))
+		hasher.Update(buf, list.GetRlp(i))
 	}
 	return hasher.Hash()
 }
diff --git a/rlp/raw.go b/rlp/raw.go
index c2a8517f62..3071e99cab 100644
--- a/rlp/raw.go
+++ b/rlp/raw.go
@@ -180,3 +180,74 @@ func readSize(b []byte, slen byte) (uint64, error) {
 	}
 	return s, nil
 }
+
+// AppendUint64 appends the RLP encoding of i to b, and returns the resulting slice.
+func AppendUint64(b []byte, i uint64) []byte {
+	if i == 0 {
+		return append(b, 0x80)
+	} else if i < 128 {
+		return append(b, byte(i))
+	}
+	switch {
+	case i < (1 << 8):
+		return append(b, 0x81, byte(i))
+	case i < (1 << 16):
+		return append(b, 0x82,
+			byte(i>>8),
+			byte(i),
+		)
+	case i < (1 << 24):
+		return append(b, 0x83,
+			byte(i>>16),
+			byte(i>>8),
+			byte(i),
+		)
+	case i < (1 << 32):
+		return append(b, 0x84,
+			byte(i>>24),
+			byte(i>>16),
+			byte(i>>8),
+			byte(i),
+		)
+	case i < (1 << 40):
+		return append(b, 0x85,
+			byte(i>>32),
+			byte(i>>24),
+			byte(i>>16),
+			byte(i>>8),
+			byte(i),
+		)
+
+	case i < (1 << 48):
+		return append(b, 0x86,
+			byte(i>>40),
+			byte(i>>32),
+			byte(i>>24),
+			byte(i>>16),
+			byte(i>>8),
+			byte(i),
+		)
+	case i < (1 << 56):
+		return append(b, 0x87,
+			byte(i>>48),
+			byte(i>>40),
+			byte(i>>32),
+			byte(i>>24),
+			byte(i>>16),
+			byte(i>>8),
+			byte(i),
+		)
+
+	default:
+		return append(b, 0x88,
+			byte(i>>56),
+			byte(i>>48),
+			byte(i>>40),
+			byte(i>>32),
+			byte(i>>24),
+			byte(i>>16),
+			byte(i>>8),
+			byte(i),
+		)
+	}
+}
diff --git a/rlp/raw_test.go b/rlp/raw_test.go
index cdae4ff088..c976c4f734 100644
--- a/rlp/raw_test.go
+++ b/rlp/raw_test.go
@@ -21,6 +21,7 @@ import (
 	"io"
 	"reflect"
 	"testing"
+	"testing/quick"
 )
 
 func TestCountValues(t *testing.T) {
@@ -239,3 +240,40 @@ func TestReadSize(t *testing.T) {
 		}
 	}
 }
+
+func TestAppendUint64(t *testing.T) {
+	tests := []struct {
+		input  uint64
+		slice  []byte
+		output string
+	}{
+		{0, nil, "80"},
+		{1, nil, "01"},
+		{2, nil, "02"},
+		{127, nil, "7F"},
+		{128, nil, "8180"},
+		{129, nil, "8181"},
+		{0xFFFFFF, nil, "83FFFFFF"},
+		{127, []byte{1, 2, 3}, "0102037F"},
+		{0xFFFFFF, []byte{1, 2, 3}, "01020383FFFFFF"},
+	}
+
+	for _, test := range tests {
+		x := AppendUint64(test.slice, test.input)
+		if !bytes.Equal(x, unhex(test.output)) {
+			t.Errorf("AppendUint64(%v, %d): got %x, want %s", test.slice, test.input, x, test.output)
+		}
+	}
+}
+
+func TestAppendUint64Random(t *testing.T) {
+	fn := func(i uint64) bool {
+		enc, _ := EncodeToBytes(i)
+		encAppend := AppendUint64(nil, i)
+		return bytes.Equal(enc, encAppend)
+	}
+	config := quick.Config{MaxCountScale: 50}
+	if err := quick.Check(fn, &config); err != nil {
+		t.Fatal(err)
+	}
+}