diff --git a/ferag.go b/ferag.go
index a4ce7be..75563fe 100644
--- a/ferag.go
+++ b/ferag.go
@@ -84,8 +84,10 @@ func (fs *FeragString) PrintOut() string {
 // AddProductReference adds a Product Reference instance to the list
 // of product references of the FeragString
 func (fs *FeragString) AddProductReference(pr *ProductReference) error {
-	fs.ProductReferencesNr++
-	pr.SetProductReferenceNumber(fs.ProductReferencesNr)
+	if pr.productReferenceNumber == 0 {
+		fs.ProductReferencesNr++
+		pr.SetProductReferenceNumber(fs.ProductReferencesNr)
+	}
 	if pr.productReferenceNumber == 1 && pr.productUsageType == 0 {
 		pr.SetProductUsageType(1)
 	}
diff --git a/product_reference.go b/product_reference.go
index 8e53de2..ddd8d0f 100644
--- a/product_reference.go
+++ b/product_reference.go
@@ -119,13 +119,17 @@ func (pr *ProductReference) SetProductName(productName string) {
 }
 
 func (pr *ProductReference) ProductReferenceNumber() string {
-	return fmt.Sprintf("+41%02d", pr.productReferenceNumber)
+	return fmt.Sprintf("+99141%03d", pr.productReferenceNumber)
 }
 
 func (pr *ProductReference) SetProductReferenceNumber(productReferenceNumber int) {
 	pr.productReferenceNumber = productReferenceNumber
 }
 
+func (pr *ProductReference) GetProductReferenceNumber() int {
+	return pr.productReferenceNumber
+}
+
 func NewProductReference() *ProductReference {
 	pr := ProductReference{
 		FeragMessage: FeragMessage{"2450", "!"},