diff --git a/corepos/db/office_trans/model.py b/corepos/db/office_trans/model.py
index d484b4b..b203240 100644
--- a/corepos/db/office_trans/model.py
+++ b/corepos/db/office_trans/model.py
@@ -32,7 +32,8 @@ Base = orm.declarative_base()
 
 
 # TODO: not sure what primary key should be for this?  am trying a
-# composite one so far, we'll see...
+# composite one so far, we'll see...cf. also andy's comments in
+# https://github.com/CORE-POS/IS4C/pull/1189#issuecomment-1597481138
 class StockPurchase(Base):
     """
     Represents a member equity payment.
@@ -43,13 +44,13 @@ class StockPurchase(Base):
 
     amount = sa.Column('stockPurchase', sa.Numeric(precision=10, scale=2), nullable=True)
 
-    datetime = sa.Column('tdate', sa.DateTime(), nullable=True, primary_key=True)
+    datetime = sa.Column('tdate', sa.DateTime(), nullable=True, primary_key=True, autoincrement=False)
 
     transaction_number = sa.Column('trans_num', sa.String(length=50), nullable=True, primary_key=True)
 
     transaction_id = sa.Column('trans_id', sa.Integer(), nullable=True)
 
-    department_number = sa.Column('dept', sa.Integer(), nullable=True)
+    department_number = sa.Column('dept', sa.Integer(), nullable=True, primary_key=True, autoincrement=False)
 
     def __str__(self):
         return f"#{self.card_number} for ${self.amount}"