diff --git a/src/main/java/org/qortal/list/ResourceList.java b/src/main/java/org/qortal/list/ResourceList.java
index fbdc8470..099aa168 100644
--- a/src/main/java/org/qortal/list/ResourceList.java
+++ b/src/main/java/org/qortal/list/ResourceList.java
@@ -13,6 +13,7 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 public class ResourceList {
@@ -20,7 +21,7 @@ public class ResourceList {
     private static final Logger LOGGER = LogManager.getLogger(ResourceList.class);
 
     private String name;
-    private List<String> list = new ArrayList<>();
+    private List<String> list = Collections.synchronizedList(new ArrayList<>());
 
     /**
      * ResourceList
diff --git a/src/main/java/org/qortal/list/ResourceListManager.java b/src/main/java/org/qortal/list/ResourceListManager.java
index 4d4d559d..4182f87c 100644
--- a/src/main/java/org/qortal/list/ResourceListManager.java
+++ b/src/main/java/org/qortal/list/ResourceListManager.java
@@ -5,6 +5,7 @@ import org.apache.logging.log4j.Logger;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 
@@ -13,7 +14,7 @@ public class ResourceListManager {
     private static final Logger LOGGER = LogManager.getLogger(ResourceListManager.class);
 
     private static ResourceListManager instance;
-    private List<ResourceList> lists = new ArrayList<>();
+    private List<ResourceList> lists = Collections.synchronizedList(new ArrayList<>());
 
 
     public ResourceListManager() {