diff --git a/purchase.py b/purchase.py
index 13e8420cd1..5d31c1db09 100644
--- a/purchase.py
+++ b/purchase.py
@@ -122,7 +122,7 @@ class PurchaseLine:
             if field.startswith('analytic_account_'):
                 if vals[field]:
                     selection_vals.setdefault('accounts', [])
-                    selection_vals['accounts'].append(('add', vals[field]))
+                    selection_vals['accounts'].append(('add', [vals[field]]))
                 del vals[field]
         if vals.get('analytic_accounts'):
             Selection.write([Selection(vals['analytic_accounts'])],