diff --git a/django_etebase/serializers.py b/django_etebase/serializers.py
index 3f1b084..908f126 100644
--- a/django_etebase/serializers.py
+++ b/django_etebase/serializers.py
@@ -382,7 +382,12 @@ class AuthenticationSignupSerializer(serializers.Serializer):
         user_data = validated_data.pop('user')
 
         with transaction.atomic():
-            instance, _ = User.objects.get_or_create(**user_data)
+            try:
+                instance = User.objects.get_by_natural_key(user_data['username'])
+            except User.DoesNotExist:
+                # Create the user and save the casing the user chose as the first name
+                instance = User.objects.create_user(**user_data, first_name=user_data['username'])
+
             if hasattr(instance, 'userinfo'):
                 raise serializers.ValidationError('User already exists')
 
diff --git a/myauth/models.py b/myauth/models.py
index 4afc27c..4046b2f 100644
--- a/myauth/models.py
+++ b/myauth/models.py
@@ -1,4 +1,4 @@
-from django.contrib.auth.models import AbstractUser
+from django.contrib.auth.models import AbstractUser, UserManager as DjangoUserManager
 from django.core import validators
 from django.db import models
 from django.utils.deconstruct import deconstructible
@@ -15,9 +15,16 @@ class UnicodeUsernameValidator(validators.RegexValidator):
     flags = 0
 
 
+class UserManager(DjangoUserManager):
+    def get_by_natural_key(self, username):
+        return self.get(**{self.model.USERNAME_FIELD + '__iexact': username})
+
+
 class User(AbstractUser):
     username_validator = UnicodeUsernameValidator()
 
+    objects = UserManager()
+
     username = models.CharField(
         _('username'),
         max_length=150,
@@ -28,3 +35,7 @@ class User(AbstractUser):
             'unique': _("A user with that username already exists."),
         },
     )
+
+    @classmethod
+    def normalize_username(cls, username):
+        return super().normalize_username(username).lower()