diff --git a/phase4-peppol-client/src/main/java/com/helger/phase4/peppol/Phase4PeppolSendingReport.java b/phase4-peppol-client/src/main/java/com/helger/phase4/peppol/Phase4PeppolSendingReport.java
index 5c790b8a0..979474b3c 100644
--- a/phase4-peppol-client/src/main/java/com/helger/phase4/peppol/Phase4PeppolSendingReport.java
+++ b/phase4-peppol-client/src/main/java/com/helger/phase4/peppol/Phase4PeppolSendingReport.java
@@ -23,6 +23,7 @@
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.NotThreadSafe;
 
 import com.helger.commons.collection.impl.CommonsArrayList;
 import com.helger.commons.collection.impl.ICommonsList;
@@ -61,6 +62,7 @@
  * @author Philip Helger
  * @since 3.0.5
  */
+@NotThreadSafe
 public class Phase4PeppolSendingReport
 {
   // State params