diff --git a/audio/audio.go b/audio/audio.go
index 250dd501c..78612398d 100644
--- a/audio/audio.go
+++ b/audio/audio.go
@@ -262,7 +262,7 @@ func (c *Context) loop() {
 		c.pingCount--
 		c.m.Unlock()
 		c.frames++
-		clock.Tick()
+		clock.Inc()
 		bytesPerFrame := c.sampleRate * bytesPerSample * channelNum / loop.FPS
 		l := (c.frames * int64(bytesPerFrame)) - c.writtenBytes
 		l &= mask
diff --git a/internal/clock/clock.go b/internal/clock/clock.go
index 956f0cef0..4307c6cbd 100644
--- a/internal/clock/clock.go
+++ b/internal/clock/clock.go
@@ -15,32 +15,63 @@
 package clock
 
 import (
+	"time"
+
 	"github.com/hajimehoshi/ebiten/internal/sync"
 )
 
 var (
-	m     sync.Mutex
-	valid bool
-	now   int64
+	m        sync.Mutex
+	valid    bool
+	tick     int64
+	lastTick int64
+	frames   int64
 )
 
-func IsValid() bool {
-	m.Lock()
-	v := valid
-	m.Unlock()
-	return v
-}
-
-func Tick() {
+func Inc() {
 	m.Lock()
 	valid = true
-	now++
+	tick++
 	m.Unlock()
 }
 
-func Now() int64 {
+func Frames(timeDuration time.Duration, fps int) (int, bool) {
 	m.Lock()
-	n := now
-	m.Unlock()
-	return n
+	defer m.Unlock()
+
+	count := 0
+
+	sync := false
+	if valid && lastTick != tick {
+		if frames < tick {
+			count = int(tick - frames)
+		}
+		lastTick = tick
+		sync = true
+	} else {
+		// Use system clock when
+		// 1) Inc() is not called, or
+		// 2) tick is not updated yet.
+		// As tick can be updated discountinuously, use system clock supplementarily.
+
+		if int64(timeDuration) > 5*int64(time.Second)/int64(fps) {
+			// The previous time is too old. Let's assume that the window was unfocused.
+			return 0, true
+		}
+		count = int(int64(timeDuration) * int64(fps) / int64(time.Second))
+	}
+
+	// Stabilize FPS.
+	if count == 0 && (int64(time.Second)/int64(fps)/2) < int64(timeDuration) {
+		count = 1
+	}
+	if count == 2 && (int64(time.Second)/int64(fps)*3/2) > int64(timeDuration) {
+		count = 1
+	}
+	if count > 3 {
+		count = 3
+	}
+
+	frames += int64(count)
+	return count, sync
 }
diff --git a/internal/loop/run.go b/internal/loop/run.go
index 16e037a73..1b1e5b628 100644
--- a/internal/loop/run.go
+++ b/internal/loop/run.go
@@ -34,11 +34,9 @@ func CurrentFPS() float64 {
 type runContext struct {
 	currentFPS     float64
 	runningSlowly  bool
-	frames         int64
 	framesForFPS   int64
 	lastUpdated    int64
 	lastFPSUpdated int64
-	lastClockFrame int64
 	ping           func()
 	m              sync.RWMutex
 }
@@ -81,42 +79,12 @@ func End() {
 }
 
 func (c *runContext) updateCount(now int64) int {
-	count := 0
-	sync := false
-
 	t := now - c.lastUpdated
 	if t < 0 {
 		return 0
 	}
 
-	if clock.IsValid() && c.lastClockFrame != clock.Now() {
-		sync = true
-		f := clock.Now()
-		if c.frames < f {
-			count = int(f - c.frames)
-		}
-		c.lastClockFrame = f
-	} else {
-		if t > 5*int64(time.Second)/int64(FPS) {
-			// The previous time is too old. Let's assume that the window was unfocused.
-			count = 0
-			sync = true
-		} else {
-			count = int(t * int64(FPS) / int64(time.Second))
-		}
-	}
-
-	// Stabilize FPS.
-	if count == 0 && (int64(time.Second)/int64(FPS)/2) < t {
-		count = 1
-	}
-	if count == 2 && (int64(time.Second)/int64(FPS)*3/2) > t {
-		count = 1
-	}
-
-	if count > 3 {
-		count = 3
-	}
+	count, sync := clock.Frames(time.Duration(t), FPS)
 
 	if sync {
 		c.lastUpdated = now
@@ -124,7 +92,6 @@ func (c *runContext) updateCount(now int64) int {
 		c.lastUpdated += int64(count) * int64(time.Second) / int64(FPS)
 	}
 
-	c.frames += int64(count)
 	return count
 }