diff --git a/src/pretix/presale/views/customer.py b/src/pretix/presale/views/customer.py
index e3075ca5e..8ec30e025 100644
--- a/src/pretix/presale/views/customer.py
+++ b/src/pretix/presale/views/customer.py
@@ -720,7 +720,7 @@ class SSOLoginReturnView(RedirectBackMixin, View):
             raise Http404("Unknown SSO method.")
 
         identifier = hashlib.sha256(
-            profile['uid'].encode() + b'@' + str(self.provider.pk).encode()
+            str(profile['uid']).encode() + b'@' + str(self.provider.pk).encode()
         ).hexdigest().upper()[:settings.ENTROPY['customer_identifier']]
         if "1" not in identifier and "0" not in identifier:
             # This is a hack to make sure the hash space does not overlap with the random identifiers generated by
@@ -753,7 +753,7 @@ class SSOLoginReturnView(RedirectBackMixin, View):
             customer = Customer(
                 organizer=self.request.organizer,
                 identifier=identifier,
-                external_identifier=profile['uid'],
+                external_identifier=str(profile['uid']),
                 provider=self.provider,
                 email=profile['email'],
                 phone=profile.get('phone') or None,
@@ -767,7 +767,7 @@ class SSOLoginReturnView(RedirectBackMixin, View):
                 customer_created.send(customer.organizer, customer=customer)
                 customer.log_action('pretix.customer.created', user=self.request.user, data=dict(
                     identifier=identifier,
-                    external_identifier=profile['uid'],
+                    external_identifier=str(profile['uid']),
                     provider=self.provider.pk,
                     email=profile['email'],
                     phone=profile.get('phone') or None,
@@ -806,7 +806,7 @@ class SSOLoginReturnView(RedirectBackMixin, View):
                     '_source': 'provider'
                 })
 
-        if customer.external_identifier != profile['uid']:
+        if customer.external_identifier != str(profile['uid']):
             return self._fail(
                 _('Login was not successful. Error message: "{error}".').format(
                     error='identifier not unique',