diff --git a/src/main/java/com/nextcloud/common/IPV6PreferringDNS.java b/src/main/java/com/nextcloud/common/IPV6PreferringDNS.java
index 1e8f68242..632436b11 100644
--- a/src/main/java/com/nextcloud/common/IPV6PreferringDNS.java
+++ b/src/main/java/com/nextcloud/common/IPV6PreferringDNS.java
@@ -3,12 +3,13 @@
 import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.util.ArrayList;
 import java.util.Collections;
-import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+
 import okhttp3.Dns;
 
 /**
@@ -16,19 +17,19 @@
  */
 public class IPV6PreferringDNS implements Dns {
 
-        private Map<String, List<InetAddress>> cache = new HashMap<>();
+    private Map<String, ArrayList<InetAddress>> cache = new HashMap<>();
 
         @Override
         public List<InetAddress> lookup(String hostname) throws UnknownHostException {
-            List<InetAddress> addresses = cache.get(hostname.toLowerCase(Locale.ROOT));
+            ArrayList<InetAddress> addresses = cache.get(hostname.toLowerCase(Locale.ROOT));
 
             if (addresses != null) {
                 return addresses;
             }
 
-            addresses = Dns.SYSTEM.lookup(hostname);
+            addresses = new ArrayList<>(Dns.SYSTEM.lookup(hostname));
             Collections.sort(addresses, (address1, address2) -> {
-                if(address1 instanceof Inet4Address) {
+                if (address1 instanceof Inet4Address) {
                     return 1;
                 } else {
                     return -1;
@@ -38,4 +39,4 @@ public List<InetAddress> lookup(String hostname) throws UnknownHostException {
 
             return addresses;
         }
-    }
\ No newline at end of file
+    }