diff --git a/lib/valvat/utils.rb b/lib/valvat/utils.rb
index b92774e..7a306d4 100644
--- a/lib/valvat/utils.rb
+++ b/lib/valvat/utils.rb
@@ -13,7 +13,7 @@ def self.split(vat)
     end
 
     def self.normalize(vat)
-      vat.upcase.gsub(NORMALIZE_PATTERN, "")
+      vat.to_s.upcase.gsub(NORMALIZE_PATTERN, "")
     end
 
     def self.vat_country_to_iso_country(vat_country)