diff --git a/app/src/main/kotlin/com/simplemobiletools/flashlight/helpers/SleepTimer.kt b/app/src/main/kotlin/com/simplemobiletools/flashlight/helpers/SleepTimer.kt
index a17c9a3..ebc6330 100644
--- a/app/src/main/kotlin/com/simplemobiletools/flashlight/helpers/SleepTimer.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/flashlight/helpers/SleepTimer.kt
@@ -26,7 +26,7 @@ object SleepTimer {
     }
 
     context(Context)
-    fun startTimer() {
+    fun startTimer() = synchronized(this@SleepTimer) {
         val millisInFuture = config.sleepInTS - System.currentTimeMillis() + 1000L
         sleepTimer?.cancel()
         sleepTimer = object : CountDownTimer(millisInFuture, 1000) {