diff --git a/addons/account/models/res_users.py b/addons/account/models/res_users.py
index d564746dfd6..0cf9d85cedb 100644
--- a/addons/account/models/res_users.py
+++ b/addons/account/models/res_users.py
@@ -19,8 +19,9 @@ class Users(models.Model):
             # A user cannot be in a non-existant group
             return
 
-        if self._has_multiple_groups([g1.id, g2.id]):
-            raise ValidationError(_("A user cannot have both Tax B2B and Tax B2C.\n"
-                                    "You should go in General Settings, and choose to display Product Prices\n"
-                                    "either in 'Tax-Included' or in 'Tax-Excluded' mode\n"
-                                    "(or switch twice the mode if you are already in the desired one)."))
+        for user in self:
+            if user._has_multiple_groups([g1.id, g2.id]):
+                raise ValidationError(_("A user cannot have both Tax B2B and Tax B2C.\n"
+                                        "You should go in General Settings, and choose to display Product Prices\n"
+                                        "either in 'Tax-Included' or in 'Tax-Excluded' mode\n"
+                                        "(or switch twice the mode if you are already in the desired one)."))