diff --git a/src/main/java/org/caosdb/server/entity/Message.java b/src/main/java/org/caosdb/server/entity/Message.java
index bdf6488d15a1d77b3038ece18541cab78ee9c805..63cf8210becc916447ac9e64cebcf094e179f865 100644
--- a/src/main/java/org/caosdb/server/entity/Message.java
+++ b/src/main/java/org/caosdb/server/entity/Message.java
@@ -21,6 +21,8 @@
  */
 package org.caosdb.server.entity;
 
+import java.util.HashMap;
+import java.util.Map;
 import org.caosdb.api.entity.v1.MessageCode;
 import org.caosdb.server.entity.xml.ToElementable;
 import org.jdom2.Element;
@@ -32,6 +34,22 @@ public class Message extends Exception implements Comparable<Message>, ToElement
   private final String description;
   private final String body;
 
+  @Deprecated private static final Map<MessageCode, String> legacy_codes_mapping = new HashMap<>();
+
+  static {
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_ENTITY_HAS_BEEN_DELETED_SUCCESSFULLY, "10");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_ATOMICITY_ERROR, "12");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_ENTITY_DOES_NOT_EXIST, "101");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_PROPERTY_HAS_NO_DATA_TYPE, "110");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_ENTITY_HAS_UNQUALIFIED_PROPERTIES, "114");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_ENTITY_HAS_UNQUALIFIED_PARENTS, "116");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_WARNING_OCCURED, "128");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_ENTITY_NAME_IS_NOT_UNIQUE, "152");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_REQUIRED_BY_UNQUALIFIED, "192");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_REFERENCED_ENTITY_DOES_NOT_EXIST, "235");
+    legacy_codes_mapping.put(MessageCode.MESSAGE_CODE_AUTHORIZATION_ERROR, "403");
+  }
+
   private static final long serialVersionUID = 1837110172902899264L;
 
   public enum MessageType {
@@ -49,7 +67,7 @@ public class Message extends Exception implements Comparable<Message>, ToElement
   public String toString() {
     return this.type.toString()
         + " ("
-        + this.code.toString()
+        + (this.code != null ? this.code.toString() : "")
         + ") - "
         + (this.description != null ? this.description : "");
   }
@@ -129,8 +147,12 @@ public class Message extends Exception implements Comparable<Message>, ToElement
 
   public Element toElement() {
     final Element e = new Element(this.type);
-    if (this.code != null) {
-      e.setAttribute("code", this.code.toString());
+    if (this.code != null && this.code != MessageCode.MESSAGE_CODE_UNKNOWN) {
+      if (legacy_codes_mapping.containsKey(this.code)) {
+        e.setAttribute("code", legacy_codes_mapping.get(this.code));
+      } else {
+        e.setAttribute("code", Integer.toString(this.code.getNumber()));
+      }
     }
     if (this.description != null) {
       e.setAttribute("description", this.description);