What version of Go are you using (go version)?

go 1.16.beta1

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

darwin/amd64

What did you do?

package main

import (
	"encoding/json"
	"fmt"
	"strings"
)

func main() {
	s := `01`
	sr := strings.NewReader(s)
	dec := json.NewDecoder(sr)
	var f float64
	err := dec.Decode(&f)
	fmt.Println(f, err)
}

What did you expect to see?

an error related to an invalid number

What did you see instead?

0 <nil>