diff --git a/dataformat-aasx/src/main/java/org/eclipse/digitaltwin/aas4j/v3/dataformat/aasx/AASXSerializer.java b/dataformat-aasx/src/main/java/org/eclipse/digitaltwin/aas4j/v3/dataformat/aasx/AASXSerializer.java
index f17f5b54..b11052e8 100644
--- a/dataformat-aasx/src/main/java/org/eclipse/digitaltwin/aas4j/v3/dataformat/aasx/AASXSerializer.java
+++ b/dataformat-aasx/src/main/java/org/eclipse/digitaltwin/aas4j/v3/dataformat/aasx/AASXSerializer.java
@@ -174,7 +174,8 @@ private void saveAASX(OutputStream os, OPCPackage rootPackage) throws IOExceptio
      * @return UUID
      */
     private String createUniqueID() {
-        return UUID.randomUUID().toString();
+		// The unique id has to start with a letter (cf. xs:ID). UUIDs do this only sometimes.
+		return "A" + UUID.randomUUID().toString();
     }
 
     /**
@@ -285,4 +286,4 @@ private String preparePath(String path) {
         return path;
     }
 
-}
\ No newline at end of file
+}