diff --git a/server/mergin/auth/models.py b/server/mergin/auth/models.py
index e9cfb61b..85741470 100644
--- a/server/mergin/auth/models.py
+++ b/server/mergin/auth/models.py
@@ -203,6 +203,8 @@ 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]
         # 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 167fe5f3..f70dbd53 100644
--- a/server/mergin/tests/test_auth.py
+++ b/server/mergin/tests/test_auth.py
@@ -117,6 +117,7 @@ def test_logout(client):
         400,
     ),  # tests with upper case, but email already exists
     (" mergin@mergin.com  ", "#pwd123", 400),  # invalid password
+    ("verylonglonglonglonglonglonglongemail@example.com", "#pwd1234", 201),
 ]
 
 
@@ -851,6 +852,10 @@ 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"
+    )
 
 
 def test_server_usage(client):