Please answer these questions before submitting your issue. Thanks!

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

go1.9 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

Windows 10 64bits

What did you do?

https://play.golang.org/p/9lzcI2y9Za

package main

import (
	"fmt"
	"strings"
	"sync"
)

func main() {
	log := []string{}
	wg := sync.WaitGroup{}
	wg.Add(2)
	ch := make(chan int, 5)
	go func() {
		for i := 0; i < 15; i++ {
			log = append(log, fmt.Sprintf("Out %d", i))
			ch <- i
		}
		wg.Done()
	}()

	go func() {
		for i := 0; i < 15; i++ {
			x := <-ch
			log = append(log, fmt.Sprintf("In %d", x))
		}

		wg.Done()
	}()
	wg.Wait()
	fmt.Println(strings.Join(log, "\n"))
}

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best

What did you expect to see?

Out 0
Out 1
Out 2
Out 3
Out 4
In 0
In 1
In 2
In 3
In 4
Out 5
Out 6
Out 7
Out 8
Out 9
In 5
In 6
In 7
In 8
In 9
Out 10
Out 11
Out 12
Out 13
Out 14
In 10
In 11
In 12
In 13
In 14

What did you see instead?

Out 0
Out 1
Out 2
Out 3
Out 4
Out 5
Out 6
In 0
In 1
In 2
In 3
In 4
In 5
In 6
Out 7
Out 8
Out 9
Out 10
Out 11
Out 12
Out 13
In 7
In 8
In 9
In 10
In 11
In 12
In 13
Out 14
In 14

Try setting the buffer size to 0 and you will observe that the buffer has the size 2. I think that the real buffer size of this definition : ch := make(chan int, N) is N+2
It is normal ? or an issue ?