diff --git a/server/mergin/auth/forms.py b/server/mergin/auth/forms.py
index b4c2a14d..b45638eb 100644
--- a/server/mergin/auth/forms.py
+++ b/server/mergin/auth/forms.py
@@ -15,7 +15,7 @@
     EqualTo,
 )
 
-from .models import User
+from .models import MAX_USERNAME_LENGTH, User
 from ..app import UpdateForm, CustomStringField
 
 
@@ -87,7 +87,10 @@ class LoginForm(FlaskForm):
 class RegisterUserForm(FlaskForm):
     username = CustomStringField(
         "Username",
-        validators=[validators.Length(min=4, max=25), username_validation],
+        validators=[
+            validators.Length(min=4, max=MAX_USERNAME_LENGTH),
+            username_validation,
+        ],
     )
     email = CustomStringField(
         "Email Address",
diff --git a/server/mergin/auth/models.py b/server/mergin/auth/models.py
index e580e814..31499ad3 100644
--- a/server/mergin/auth/models.py
+++ b/server/mergin/auth/models.py
@@ -14,6 +14,8 @@
 from ..sync.models import ProjectUser
 from ..sync.utils import get_user_agent, get_ip, get_device_id, is_reserved_word
 
+MAX_USERNAME_LENGTH = 50
+
 
 class User(db.Model):
     id = db.Column(db.Integer, primary_key=True)
@@ -203,8 +205,8 @@ def generate_username(cls, email: str) -> Optional[str]:
         ).ljust(4, "0")
         # additional check for reserved words
         username = f"{username}0" if is_reserved_word(username) else username
-        # some value until 25 + space for suffix
-        username = username[:22]
+        # keep some space for suffix
+        username = username[: MAX_USERNAME_LENGTH - 3]
         # check if we already do not have existing usernames
         query = db.session.execute(
             text(
diff --git a/server/mergin/tests/test_auth.py b/server/mergin/tests/test_auth.py
index c8b9a682..a5217f6a 100644
--- a/server/mergin/tests/test_auth.py
+++ b/server/mergin/tests/test_auth.py
@@ -851,10 +851,13 @@ def test_username_generation(client):
 
     user = add_user("support1", "user")
     assert User.generate_username("support@example.com") == "support0"
-    assert (
-        User.generate_username("verylonglonglonglonglong@example.com")
-        == "verylonglonglonglonglo"
-    )
+
+    # test long emails
+    username = "a" * 25
+    assert User.generate_username(f"{username}@example.com") == username
+    # shortened version
+    username = "a" * 50
+    assert User.generate_username(f"{username}@example.com") == username[:47]
 
     # test username generation with existing user, case insensitive
     user = add_user("Testuser")