diff --git a/internal/encoder/compact.go b/internal/encoder/compact.go
index 718d1cc..d70d9e3 100644
--- a/internal/encoder/compact.go
+++ b/internal/encoder/compact.go
@@ -7,7 +7,6 @@ import (
 	"unsafe"
 
 	"github.com/goccy/go-json/internal/errors"
-	"github.com/goccy/go-json/internal/runtime"
 )
 
 var (
@@ -29,8 +28,11 @@ func Compact(buf *bytes.Buffer, src []byte, escape bool) error {
 	if len(src) == 0 {
 		return errors.ErrUnexpectedEndOfJSON("", 0)
 	}
-	dst := make([]byte, 0, len(src))
-	dst, err := compact(dst, src, escape)
+	buf.Grow(len(src))
+	dst := buf.Bytes()
+	newSrc := make([]byte, len(src)+1) // append nul byte to the end
+	copy(newSrc, src)
+	dst, err := compact(dst, newSrc, escape)
 	if err != nil {
 		return err
 	}
@@ -41,12 +43,10 @@ func Compact(buf *bytes.Buffer, src []byte, escape bool) error {
 }
 
 func compact(dst, src []byte, escape bool) ([]byte, error) {
-	src = append(src, nul)
 	buf, _, err := compactValue(dst, src, 0, escape)
 	if err != nil {
 		return nil, err
 	}
-	(*runtime.SliceHeader)(unsafe.Pointer(&src)).Len--
 	return buf, nil
 }
 
diff --git a/internal/encoder/encoder.go b/internal/encoder/encoder.go
index 2c0a30c..8815d62 100644
--- a/internal/encoder/encoder.go
+++ b/internal/encoder/encoder.go
@@ -306,6 +306,7 @@ func MapLen(m unsafe.Pointer) int
 
 type RuntimeContext struct {
 	Buf        []byte
+	MarshalBuf []byte
 	Ptrs       []uintptr
 	KeepRefs   []unsafe.Pointer
 	SeenPtr    []uintptr
@@ -413,7 +414,7 @@ func AppendNumber(b []byte, n json.Number) ([]byte, error) {
 	return b, nil
 }
 
-func AppendMarshalJSON(code *Opcode, b []byte, v interface{}, escape bool) ([]byte, error) {
+func AppendMarshalJSON(ctx *RuntimeContext, code *Opcode, b []byte, v interface{}, escape bool) ([]byte, error) {
 	rv := reflect.ValueOf(v) // convert by dynamic interface type
 	if code.AddrForMarshaler {
 		if rv.CanAddr() {
@@ -433,10 +434,13 @@ func AppendMarshalJSON(code *Opcode, b []byte, v interface{}, escape bool) ([]by
 	if err != nil {
 		return nil, &errors.MarshalerError{Type: reflect.TypeOf(v), Err: err}
 	}
-	compactedBuf, err := compact(b, bb, escape)
+	marshalBuf := ctx.MarshalBuf[:0]
+	marshalBuf = append(append(marshalBuf, bb...), nul)
+	compactedBuf, err := compact(b, marshalBuf, escape)
 	if err != nil {
 		return nil, &errors.MarshalerError{Type: reflect.TypeOf(v), Err: err}
 	}
+	ctx.MarshalBuf = marshalBuf
 	return compactedBuf, nil
 }
 
diff --git a/internal/encoder/vm/vm.go b/internal/encoder/vm/vm.go
index b4b80b6..ac2997a 100644
--- a/internal/encoder/vm/vm.go
+++ b/internal/encoder/vm/vm.go
@@ -273,7 +273,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if code.IsNilableType && code.Indirect {
 				p = ptrToPtr(p)
 			}
-			bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+			bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 			if err != nil {
 				return nil, err
 			}
@@ -2718,7 +2718,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -2762,7 +2762,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -2807,7 +2807,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)
-				bb, err := appendMarshalJSON(code, b, iface, false)
+				bb, err := appendMarshalJSON(ctx, code, b, iface, false)
 				if err != nil {
 					return nil, err
 				}
@@ -2847,7 +2847,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -2887,7 +2887,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -3628,7 +3628,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -3652,7 +3652,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				break
 			}
 			b = append(b, code.Key...)
-			bb, err := appendMarshalJSON(code, b, iface, false)
+			bb, err := appendMarshalJSON(ctx, code, b, iface, false)
 			if err != nil {
 				return nil, err
 			}
@@ -3665,7 +3665,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -3678,7 +3678,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p = ptrToNPtr(p+code.Offset, code.PtrNum)
 			if p != 0 {
 				b = append(b, code.Key...)
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
diff --git a/internal/encoder/vm_debug/vm.go b/internal/encoder/vm_debug/vm.go
index b78d813..88809f7 100644
--- a/internal/encoder/vm_debug/vm.go
+++ b/internal/encoder/vm_debug/vm.go
@@ -286,7 +286,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if code.IsNilableType && code.Indirect {
 				p = ptrToPtr(p)
 			}
-			bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+			bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 			if err != nil {
 				return nil, err
 			}
@@ -2731,7 +2731,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -2775,7 +2775,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -2820,7 +2820,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)
-				bb, err := appendMarshalJSON(code, b, iface, false)
+				bb, err := appendMarshalJSON(ctx, code, b, iface, false)
 				if err != nil {
 					return nil, err
 				}
@@ -2860,7 +2860,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -2900,7 +2900,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				code = code.NextField
 			} else {
 				b = append(b, code.Key...)
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -3641,7 +3641,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -3665,7 +3665,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				break
 			}
 			b = append(b, code.Key...)
-			bb, err := appendMarshalJSON(code, b, iface, false)
+			bb, err := appendMarshalJSON(ctx, code, b, iface, false)
 			if err != nil {
 				return nil, err
 			}
@@ -3678,7 +3678,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
@@ -3691,7 +3691,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p = ptrToNPtr(p+code.Offset, code.PtrNum)
 			if p != 0 {
 				b = append(b, code.Key...)
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), false)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), false)
 				if err != nil {
 					return nil, err
 				}
diff --git a/internal/encoder/vm_escaped/vm.go b/internal/encoder/vm_escaped/vm.go
index 846119b..1daec9d 100644
--- a/internal/encoder/vm_escaped/vm.go
+++ b/internal/encoder/vm_escaped/vm.go
@@ -273,7 +273,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if code.IsNilableType && code.Indirect {
 				p = ptrToPtr(p)
 			}
-			bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+			bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 			if err != nil {
 				return nil, err
 			}
@@ -2718,7 +2718,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}
@@ -2762,7 +2762,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}
@@ -2807,7 +2807,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				code = code.NextField
 			} else {
 				b = append(b, code.EscapedKey...)
-				bb, err := appendMarshalJSON(code, b, iface, true)
+				bb, err := appendMarshalJSON(ctx, code, b, iface, true)
 				if err != nil {
 					return nil, err
 				}
@@ -2847,7 +2847,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}
@@ -2887,7 +2887,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				code = code.NextField
 			} else {
 				b = append(b, code.EscapedKey...)
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}
@@ -3628,7 +3628,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 && code.Nilcheck {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}
@@ -3652,7 +3652,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 				break
 			}
 			b = append(b, code.EscapedKey...)
-			bb, err := appendMarshalJSON(code, b, iface, true)
+			bb, err := appendMarshalJSON(ctx, code, b, iface, true)
 			if err != nil {
 				return nil, err
 			}
@@ -3665,7 +3665,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			if p == 0 {
 				b = appendNull(b)
 			} else {
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}
@@ -3678,7 +3678,7 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet, opt
 			p = ptrToNPtr(p+code.Offset, code.PtrNum)
 			if p != 0 {
 				b = append(b, code.EscapedKey...)
-				bb, err := appendMarshalJSON(code, b, ptrToInterface(code, p), true)
+				bb, err := appendMarshalJSON(ctx, code, b, ptrToInterface(code, p), true)
 				if err != nil {
 					return nil, err
 				}