diff --git a/modules/product_classification_taxonomic/product.py b/modules/product_classification_taxonomic/product.py
index ecd29b686b..d102618fe0 100644
--- a/modules/product_classification_taxonomic/product.py
+++ b/modules/product_classification_taxonomic/product.py
@@ -20,6 +20,7 @@ class Taxon(classification_tree('product.taxon'), ModelSQL, ModelView):
     'Taxon'
     __name__ = 'product.taxon'
     rank = fields.Selection([
+            (None, ""),
             ('domain', 'Domain'),
             ('kingdom', 'Kingdom'),
             ('phylum', 'Phylum'),