diff --git a/advlabdb/models.py b/advlabdb/models.py
index 63c0d92..c410e21 100644
--- a/advlabdb/models.py
+++ b/advlabdb/models.py
@@ -515,6 +515,8 @@ class Semester(db.Model):
     id = db.Column(db.Integer, primary_key=True)
     label = db.Column(db.String(10), db.CheckConstraint("label IN ('WS', 'SS')"), nullable=False)
     year = db.Column(db.Integer, db.CheckConstraint(f"year BETWEEN {MIN_YEAR} AND {MAX_YEAR}"), nullable=False)
+    # Assistants can not work in semesters that are done
+    done = db.Column(db.Boolean, default=False, nullable=False)
 
     parts = db.relationship("Part", back_populates="semester", lazy=True)
     semester_experiments = db.relationship("SemesterExperiment", back_populates="semester", lazy=True)