diff --git a/implementation/src/main/java/io/smallrye/mutiny/helpers/test/AssertSubscriber.java b/implementation/src/main/java/io/smallrye/mutiny/helpers/test/AssertSubscriber.java
index 125bebb5c..f5b047976 100644
--- a/implementation/src/main/java/io/smallrye/mutiny/helpers/test/AssertSubscriber.java
+++ b/implementation/src/main/java/io/smallrye/mutiny/helpers/test/AssertSubscriber.java
@@ -5,8 +5,6 @@
 import static java.time.Duration.ofSeconds;
 
 import java.time.Duration;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.concurrent.*;
@@ -67,7 +65,7 @@ public class AssertSubscriber<T> implements MultiSubscriber<T>, ContextSupport {
     /**
      * The received items.
      */
-    private final List<T> items = Collections.synchronizedList(new ArrayList<>());
+    private final List<T> items = new CopyOnWriteArrayList<>();
 
     /**
      * The received failure.