diff --git a/payment_sixpay/README.md b/payment_sixpay/README.md
index 8f0bafe6..20bab5a7 100644
--- a/payment_sixpay/README.md
+++ b/payment_sixpay/README.md
@@ -11,6 +11,7 @@ they are automatically sent back to Indico.
 ### 3.3.1
 
 - Update iso4217 dependency
+- Support longer Saferpay account IDs
 
 ### 3.3
 
diff --git a/payment_sixpay/indico_payment_sixpay/forms.py b/payment_sixpay/indico_payment_sixpay/forms.py
index 09da1e46..b3fe327c 100644
--- a/payment_sixpay/indico_payment_sixpay/forms.py
+++ b/payment_sixpay/indico_payment_sixpay/forms.py
@@ -110,10 +110,10 @@ class PluginSettingsForm(PaymentPluginSettingsFormBase):
         label=_('Account ID'),
         validators=[
             Optional(),
-            IndicoRegexp(r'^[0-9-]{0,15}$')
+            IndicoRegexp(r'^[0-9-]{0,16}$')
         ],
         description=_(
-            'Default Saferpay account ID, such as "123456-12345678". '
+            'Default Saferpay account ID, such as "1234567-12345678". '
             'Event managers will be able to override this.'
         )
     )
@@ -154,9 +154,9 @@ class EventSettingsForm(PaymentEventSettingsFormBase):
         label=_('Account ID'),
         validators=[
             DataRequired(),
-            IndicoRegexp(r'^[0-9-]{0,15}$')
+            IndicoRegexp(r'^[0-9-]{0,16}$')
         ],
-        description=_('The Saferpay account ID, such as "123456-12345678".')
+        description=_('The Saferpay account ID, such as "1234567-12345678".')
     )
     order_description = StringField(
         label=_('Order Description'),