diff --git a/l10n_es_vat_book/models/l10n_es_vat_book.py b/l10n_es_vat_book/models/l10n_es_vat_book.py
index 1cd009e9ddf..6dc30454b85 100644
--- a/l10n_es_vat_book/models/l10n_es_vat_book.py
+++ b/l10n_es_vat_book/models/l10n_es_vat_book.py
@@ -247,7 +247,7 @@ def upsert_book_line_tax(self, move_line, vat_book_line, implied_taxes):
                 continue
             key = self.get_book_line_tax_key(move_line, tax)
             if key not in tax_lines:
-                tax_lines[key] = vals
+                tax_lines[key] = vals.copy()
                 tax_lines[key]['tax_id'] = tax.id
             else:
                 tax_lines[key]['base_amount'] += vals['base_amount']