diff --git a/app/core/src/main/java/com/fsck/k9/job/MailSyncWorkerManager.kt b/app/core/src/main/java/com/fsck/k9/job/MailSyncWorkerManager.kt
index 3db9b9d66..989a42ee0 100644
--- a/app/core/src/main/java/com/fsck/k9/job/MailSyncWorkerManager.kt
+++ b/app/core/src/main/java/com/fsck/k9/job/MailSyncWorkerManager.kt
@@ -10,7 +10,7 @@ import androidx.work.workDataOf
 import com.fsck.k9.Account
 import com.fsck.k9.Clock
 import com.fsck.k9.K9
-import java.time.Duration
+import java.util.concurrent.TimeUnit
 import timber.log.Timber
 
 class MailSyncWorkerManager(private val workManager: WorkManager, val clock: Clock) {
@@ -24,9 +24,9 @@ class MailSyncWorkerManager(private val workManager: WorkManager, val clock: Clo
     fun scheduleMailSync(account: Account) {
         if (isNeverSyncInBackground()) return
 
-        getSyncIntervalIfEnabled(account)?.let { syncInterval ->
+        getSyncIntervalIfEnabled(account)?.let { syncIntervalMinutes ->
             Timber.v("Scheduling mail sync worker for %s", account.description)
-            Timber.v("  sync interval: %d minutes", syncInterval.toMinutes())
+            Timber.v("  sync interval: %d minutes", syncIntervalMinutes)
 
             val constraints = Constraints.Builder()
                 .setRequiredNetworkType(NetworkType.CONNECTED)
@@ -36,14 +36,14 @@ class MailSyncWorkerManager(private val workManager: WorkManager, val clock: Clo
             val lastSyncTime = account.lastSyncTime
             Timber.v("  last sync time: %tc", lastSyncTime)
 
-            val initialDelay = calculateInitialDelay(lastSyncTime, syncInterval)
-            Timber.v("  initial delay: %d minutes", initialDelay.toMinutes())
+            val initialDelay = calculateInitialDelay(lastSyncTime, syncIntervalMinutes)
+            Timber.v("  initial delay: %d ms", initialDelay)
 
             val data = workDataOf(MailSyncWorker.EXTRA_ACCOUNT_UUID to account.uuid)
 
-            val mailSyncRequest = PeriodicWorkRequestBuilder<MailSyncWorker>(syncInterval)
-                .setInitialDelay(initialDelay)
-                .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, INITIAL_BACKOFF_DELAY)
+            val mailSyncRequest = PeriodicWorkRequestBuilder<MailSyncWorker>(syncIntervalMinutes, TimeUnit.MINUTES)
+                .setInitialDelay(initialDelay, TimeUnit.MILLISECONDS)
+                .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, INITIAL_BACKOFF_DELAY_MINUTES, TimeUnit.MINUTES)
                 .setConstraints(constraints)
                 .setInputData(data)
                 .addTag(MAIL_SYNC_TAG)
@@ -56,23 +56,23 @@ class MailSyncWorkerManager(private val workManager: WorkManager, val clock: Clo
 
     private fun isNeverSyncInBackground() = K9.backgroundOps == K9.BACKGROUND_OPS.NEVER
 
-    private fun getSyncIntervalIfEnabled(account: Account): Duration? {
+    private fun getSyncIntervalIfEnabled(account: Account): Long? {
         val intervalMinutes = account.automaticCheckIntervalMinutes
         if (intervalMinutes <= Account.INTERVAL_MINUTES_NEVER) {
             return null
         }
 
-        return Duration.ofMinutes(intervalMinutes.toLong())
+        return intervalMinutes.toLong()
     }
 
-    private fun calculateInitialDelay(lastSyncTime: Long, syncInterval: Duration): Duration {
+    private fun calculateInitialDelay(lastSyncTime: Long, syncIntervalMinutes: Long): Long {
         val now = clock.time
-        val nextSyncTime = lastSyncTime + syncInterval.toMillis()
+        val nextSyncTime = lastSyncTime + (syncIntervalMinutes * 60L * 1000L)
 
         return if (lastSyncTime > now || nextSyncTime <= now) {
-            Duration.ZERO
+            0L
         } else {
-            Duration.ofMillis(nextSyncTime - now)
+            nextSyncTime - now
         }
     }
 
@@ -82,6 +82,6 @@ class MailSyncWorkerManager(private val workManager: WorkManager, val clock: Clo
 
     companion object {
         const val MAIL_SYNC_TAG = "MailSync"
-        private val INITIAL_BACKOFF_DELAY = Duration.ofMinutes(5)
+        private const val INITIAL_BACKOFF_DELAY_MINUTES = 5L
     }
 }