diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 579f0b4..ce6e73e 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: [ '1.15.x' ]
+        go: [ '1.15.x', '1.16.x' ]
     steps:
 
     - name: Set up Go
diff --git a/cli/cli.go b/cli/cli.go
index 6d879f4..3ab80eb 100644
--- a/cli/cli.go
+++ b/cli/cli.go
@@ -175,8 +175,8 @@ func (c *CLI) Run(args []string) int {
 
 	ex := throttle.NewExec(copyStdin)
 
-	exitC := make(chan os.Signal, 1)
-	signal.Notify(exitC, syscall.SIGTERM, syscall.SIGINT)
+	sigC := make(chan os.Signal, 1)
+	signal.Notify(sigC, syscall.SIGTERM, syscall.SIGINT)
 
 	channel := c.conf.PrimaryChannel
 	if channel == "" {
@@ -189,19 +189,19 @@ func (c *CLI) Run(args []string) int {
 		IconEmoji: c.conf.IconEmoji,
 	}
 
-	flushCallback := func(_ context.Context, output string) error {
+	flushCallback := func(output string) error {
 		param.Text = output
 		return c.sClient.PostText(context.Background(), param)
 	}
 
 	done := make(chan struct{})
 
-	doneCallback := func(ctx context.Context, output string) error {
+	doneCallback := func(output string) error {
 		defer func() {
 			done <- struct{}{}
 		}()
 
-		return flushCallback(ctx, output)
+		return flushCallback(output)
 	}
 
 	ticker := time.NewTicker(c.conf.Duration)
@@ -209,11 +209,15 @@ func (c *CLI) Run(args []string) int {
 
 	ctx, cancel := context.WithCancel(context.Background())
 
-	ex.Start(ctx, ticker.C, flushCallback, doneCallback)
+	exitC := make(chan struct{})
+	go func() {
+		ex.Start(ctx, ticker.C, flushCallback, doneCallback)
+		close(exitC)
+	}()
 
 	select {
+	case <-sigC:
 	case <-exitC:
-	case <-ex.Wait():
 	}
 	cancel()
 
diff --git a/throttle/exec.go b/throttle/exec.go
index 9f3d772..a414af8 100644
--- a/throttle/exec.go
+++ b/throttle/exec.go
@@ -51,7 +51,7 @@ func (ex *Exec) stringAndReset() string {
 	return ex.writer.String()
 }
 
-func (ex *Exec) Start(ctx context.Context, interval <-chan time.Time, flushCallback func(ctx context.Context, output string) error, doneCallback func(ctx context.Context, output string) error) {
+func (ex *Exec) Start(ctx context.Context, interval <-chan time.Time, flushCallback func(output string) error, doneCallback func(output string) error) {
 	go func() {
 		for {
 			line, _, err := ex.reader.ReadLine()
@@ -71,20 +71,23 @@ func (ex *Exec) Start(ctx context.Context, interval <-chan time.Time, flushCallb
 				panic(err)
 			}
 		}
-		ex.exitC <- struct{}{}
+		// if notify_slack receives EOF, this function will exit.
+		close(ex.exitC)
 	}()
 
-	go func() {
-		for {
-			select {
-			case <-interval:
-				flushCallback(ctx, ex.flush())
-			case <-ctx.Done():
-				doneCallback(ctx, ex.flush())
-				return
-			}
+L:
+	for {
+		select {
+		case <-interval:
+			flushCallback(ex.flush())
+		case <-ctx.Done():
+			doneCallback(ex.flush())
+			break L
+		case <-ex.Wait():
+			doneCallback(ex.flush())
+			break L
 		}
-	}()
+	}
 }
 
 func (ex *Exec) Wait() <-chan struct{} {
diff --git a/throttle/exec_test.go b/throttle/exec_test.go
index 6070266..5d67386 100644
--- a/throttle/exec_test.go
+++ b/throttle/exec_test.go
@@ -8,7 +8,7 @@ import (
 	"time"
 )
 
-func TestRun(t *testing.T) {
+func TestRun_pipeClose(t *testing.T) {
 	pr, pw := io.Pipe()
 
 	output := new(bytes.Buffer)
@@ -20,7 +20,7 @@ func TestRun(t *testing.T) {
 	count := 0
 	fc := make(chan struct{})
 
-	flushCallback := func(_ context.Context, s string) error {
+	flushCallback := func(s string) error {
 		defer func() {
 			fc <- struct{}{}
 			// to random fail from Go 1.12 or later
@@ -36,7 +36,7 @@ func TestRun(t *testing.T) {
 
 	doneCount := 0
 
-	doneCallback := func(_ context.Context, s string) error {
+	doneCallback := func(s string) error {
 		defer func() {
 			fc <- struct{}{}
 		}()
@@ -48,7 +48,11 @@ func TestRun(t *testing.T) {
 		return nil
 	}
 
-	ex.Start(ctx, testC, flushCallback, doneCallback)
+	exitC := make(chan struct{})
+	go func() {
+		ex.Start(ctx, testC, flushCallback, doneCallback)
+		close(exitC)
+	}()
 
 	testC <- time.Time{}
 	<-fc
@@ -82,7 +86,7 @@ func TestRun(t *testing.T) {
 
 	// do not panic
 	pw.Close()
-	<-ex.Wait()
+	<-exitC
 
 	cancel()
 	<-fc