diff --git a/app/lint.xml b/app/lint.xml
index 0819b090be..8e774ae6a2 100644
--- a/app/lint.xml
+++ b/app/lint.xml
@@ -25,6 +25,7 @@
     <issue id="VectorRaster" severity="error" />
     <issue id="ButtonOrder" severity="error" />
     <issue id="ExtraTranslation" severity="warning" />
+    <issue id="UnspecifiedImmutableFlag" severity="error" />
 
     <!-- Custom lints -->
     <issue id="LogNotSignal" severity="error" />
diff --git a/app/src/main/java/org/thoughtcrime/securesms/util/AlarmSleepTimer.java b/app/src/main/java/org/thoughtcrime/securesms/util/AlarmSleepTimer.java
index 08e5fca5fa..70ea8699bc 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/util/AlarmSleepTimer.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/util/AlarmSleepTimer.java
@@ -11,6 +11,7 @@ import android.os.SystemClock;
 import androidx.core.app.AlarmManagerCompat;
 import androidx.core.content.ContextCompat;
 
+import org.signal.core.util.PendingIntentFlags;
 import org.signal.core.util.logging.Log;
 import org.whispersystems.signalservice.api.util.SleepTimer;
 
@@ -67,7 +68,7 @@ public class AlarmSleepTimer implements SleepTimer {
 
     private void setAlarm(long millis, String action) {
       final Intent        intent        = new Intent(action);
-      final PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
+      final PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, PendingIntentFlags.mutable());
       final AlarmManager  alarmManager  = ContextCompat.getSystemService(context, AlarmManager.class);
 
       Log.w(TAG, "Setting alarm to wake up in " + millis + "ms.");