diff --git a/backend/data/sqlite-database.db b/backend/data/sqlite-database.db
index 927ee53..42aca8a 100644
Binary files a/backend/data/sqlite-database.db and b/backend/data/sqlite-database.db differ
diff --git a/backend/src/rest_api.py b/backend/src/rest_api.py
index af631cb..546c49d 100644
--- a/backend/src/rest_api.py
+++ b/backend/src/rest_api.py
@@ -61,7 +61,8 @@ def register_leader() -> flask.Response:
         user_id = utils.UserHandler.get_user_by_mail(mail).user_id
         flask.session.pop("mail")
         flask.session["user_id"] = user_id
-    except (TypeError, KeyError):
+    except (TypeError, KeyError) as e:
+        print(e)
         return flask.Response("Something is missing", 422)
     except sqlite3.IntegrityError:
         return flask.Response("Mail already registered or phone number or pin code is not correct", 428)
@@ -125,6 +126,8 @@ def register() -> flask.Response:
         ))
     except TypeError:
         return flask.Response("Not all details provided", 422)
+    except AssertionError:
+        return flask.Response("Max 4 members", 400)
     except sqlite3.IntegrityError as error:
         error_message = str(error)
         if error_message == "UNIQUE constraint failed: users.phone_number":
diff --git a/backend/src/utils/team.py b/backend/src/utils/team.py
index d344b4b..d592da3 100644
--- a/backend/src/utils/team.py
+++ b/backend/src/utils/team.py
@@ -34,3 +34,14 @@ class TeamHandler:
         )
         cls.__connection.commit()
         return team.lastrowid if team.lastrowid else -1
+
+    @classmethod
+    def get_team_members(cls, team_id: int) -> list[int]:
+        users = cls.__cursor.execute(
+                f"""
+                SELECT user_id
+                FROM users WHERE team_id = ?;
+                """,
+                (team_id, )
+        ).fetchall()
+        return users
diff --git a/backend/src/utils/user.py b/backend/src/utils/user.py
index 85abe89..70f1f89 100644
--- a/backend/src/utils/user.py
+++ b/backend/src/utils/user.py
@@ -1,6 +1,7 @@
 import bcrypt
 from dataclasses import dataclass
 import sqlite3
+import utils
 
 
 @dataclass
@@ -66,6 +67,7 @@ class UserHandler:
         cls,
         user: User
     ) -> None:
+        assert len(utils.TeamHandler.get_team_members(user.team_id)) <= 4
         salt = bcrypt.gensalt()
         encrypted_password = bcrypt.hashpw(user.password.encode("utf-8"), salt)
         cls.__cursor.execute(