diff --git a/backend/app/models/audit_log.py b/backend/app/models/audit_log.py
index 0a84153..ef86bb5 100644
--- a/backend/app/models/audit_log.py
+++ b/backend/app/models/audit_log.py
@@ -86,7 +86,7 @@ class AuditLogSeverity(str, Enum):
 class AuditLog(BaseModel):
     """Audit log entry model."""
     
-    id: Optional[PyObjectId] = Field(default_factory=PyObjectId, alias="_id")
+    id: Optional[PyObjectId] = Field(default_factory=lambda: str(ObjectId()), alias="_id")
     
     # Core audit fields
     timestamp: datetime = Field(default_factory=datetime.utcnow)