diff --git a/decode.go b/decode.go
index b833656..31df2c3 100644
--- a/decode.go
+++ b/decode.go
@@ -39,7 +39,7 @@ func unmarshal(data []byte, v interface{}, optFuncs ...DecodeOptionFunc) error {
 	}
 	ctx := decoder.TakeRuntimeContext()
 	ctx.Buf = src
-	ctx.Option.FirstWin = false
+	ctx.Option.Flag = 0
 	for _, optFunc := range optFuncs {
 		optFunc(ctx.Option)
 	}
@@ -68,7 +68,7 @@ func unmarshalNoEscape(data []byte, v interface{}, optFuncs ...DecodeOptionFunc)
 
 	ctx := decoder.TakeRuntimeContext()
 	ctx.Buf = src
-	ctx.Option.FirstWin = false
+	ctx.Option.Flag = 0
 	for _, optFunc := range optFuncs {
 		optFunc(ctx.Option)
 	}
diff --git a/internal/decoder/option.go b/internal/decoder/option.go
index a44ca55..1603512 100644
--- a/internal/decoder/option.go
+++ b/internal/decoder/option.go
@@ -1,5 +1,11 @@
 package decoder
 
+type OptionFlag int
+
+const (
+	FirstWinOption OptionFlag = 1 << iota
+)
+
 type Option struct {
-	FirstWin bool
+	Flag OptionFlag
 }
diff --git a/internal/decoder/struct.go b/internal/decoder/struct.go
index ae33bdd..70cf444 100644
--- a/internal/decoder/struct.go
+++ b/internal/decoder/struct.go
@@ -727,7 +727,7 @@ func (d *structDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsaf
 		seenFields   map[int]struct{}
 		seenFieldNum int
 	)
-	firstWin := ctx.Option.FirstWin
+	firstWin := (ctx.Option.Flag & FirstWinOption) != 0
 	if firstWin {
 		seenFields = make(map[int]struct{}, d.fieldUniqueNameNum)
 	}
diff --git a/option.go b/option.go
index d2cd3b1..60225dd 100644
--- a/option.go
+++ b/option.go
@@ -32,6 +32,6 @@ type DecodeOptionFunc func(*DecodeOption)
 
 func DecodeFieldPriorityFirstWin() DecodeOptionFunc {
 	return func(opt *DecodeOption) {
-		opt.FirstWin = true
+		opt.Flag |= decoder.FirstWinOption
 	}
 }