diff --git a/app/api/routers/misc.py b/app/api/routers/misc.py
index 5454ccf..d60f99a 100644
--- a/app/api/routers/misc.py
+++ b/app/api/routers/misc.py
@@ -107,16 +107,28 @@ def list_activity(entity_type: str = None, entity_id: int = None, user_id: int =
 
 @router.post("/milestones", response_model=schemas.MilestoneResponse, status_code=status.HTTP_201_CREATED, tags=["Milestones"])
 def create_milestone(ms: schemas.MilestoneCreate, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    import json
     # Generate milestone_code: projCode:{i:05x}
     project = db.query(models.Project).filter(models.Project.id == ms.project_id).first()
-    project_code = project.project_code if project else f"P{ms.project_id}"
+    project_code = project.project_code if project and project.project_code else f"P{ms.project_id}"
     
     # Get max milestone number for this project
     max_ms = db.query(MilestoneModel).filter(MilestoneModel.project_id == ms.project_id).order_by(MilestoneModel.id.desc()).first()
     next_num = (max_ms.id + 1) if max_ms else 1
     milestone_code = f"{project_code}:{next_num:05x}"
     
-    db_ms = MilestoneModel(**ms.model_dump())
+    data = ms.model_dump()
+    # Serialize list fields to JSON strings
+    if data.get("depend_on_milestones"):
+        data["depend_on_milestones"] = json.dumps(data["depend_on_milestones"])
+    else:
+        data["depend_on_milestones"] = None
+    if data.get("depend_on_tasks"):
+        data["depend_on_tasks"] = json.dumps(data["depend_on_tasks"])
+    else:
+        data["depend_on_tasks"] = None
+    
+    db_ms = MilestoneModel(**data)
     db_ms.milestone_code = milestone_code
     db.add(db_ms)
     db.commit()