diff --git a/snowexsql/tables/instrument.py b/snowexsql/tables/instrument.py
index 321b772..3435eba 100644
--- a/snowexsql/tables/instrument.py
+++ b/snowexsql/tables/instrument.py
@@ -22,7 +22,7 @@ def instrument_id(cls):
         return Column(
             Integer,
             ForeignKey('public.instruments.id'),
-            index=True, nullable=False
+            index=True, nullable=True
         )
 
     @declared_attr