diff --git a/nailgun/nailgun/db/sqlalchemy/models/base.py b/nailgun/nailgun/db/sqlalchemy/models/base.py
index 21a78e0e13..70acce8f89 100644
--- a/nailgun/nailgun/db/sqlalchemy/models/base.py
+++ b/nailgun/nailgun/db/sqlalchemy/models/base.py
@@ -23,6 +23,7 @@ from sqlalchemy import DateTime
 from sqlalchemy import Integer
 
 from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.ext.mutable import MutableDict
 from sqlalchemy.orm.base import object_state
 
 from nailgun.db import deadlock_detector as dd
@@ -55,5 +56,5 @@ class CapacityLog(Base):
     __tablename__ = 'capacity_log'
 
     id = Column(Integer, primary_key=True)
-    report = Column(JSON)
+    report = Column(MutableDict.as_mutable(JSON))
     datetime = Column(DateTime, default=lambda: datetime.now())