diff --git a/archaius-core/src/main/java/com/netflix/config/ConcurrentCompositeConfiguration.java b/archaius-core/src/main/java/com/netflix/config/ConcurrentCompositeConfiguration.java
index f9a76f60..1cafcad2 100644
--- a/archaius-core/src/main/java/com/netflix/config/ConcurrentCompositeConfiguration.java
+++ b/archaius-core/src/main/java/com/netflix/config/ConcurrentCompositeConfiguration.java
@@ -117,7 +117,7 @@ public Set<String> getUsedProperties() {
         return usedProperties;
     }
 
-    private Set<String> usedProperties = new HashSet<>();
+    private Set<String> usedProperties = ConcurrentHashMap.newKeySet();
 
     private List<AbstractConfiguration> configList = new CopyOnWriteArrayList<AbstractConfiguration>();