diff --git a/espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/api/Ids.java b/espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/api/Ids.java
index 7e580701e914..8e2526b812fd 100644
--- a/espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/api/Ids.java
+++ b/espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/api/Ids.java
@@ -47,7 +47,7 @@ public final class Ids<T> {
      * All entities stored while communicating with the debugger. The array will be expanded
      * whenever an ID for a new entity is requested.
      */
-    private WeakReference<T>[] objects;
+    private volatile WeakReference<T>[] objects;
 
     /**
      * A special object representing the null value. This object must be passed on by the