diff --git a/jey_erp/custom_fields.py b/jey_erp/custom_fields.py
index a72d681..eb00ac3 100644
--- a/jey_erp/custom_fields.py
+++ b/jey_erp/custom_fields.py
@@ -1101,7 +1101,10 @@ def create_custom_fields():
                 # hid the column and JS re-toggled `hidden`, which broke the grid
                 # layout — so depends_on is intentionally cleared here.
                 depends_on='',
-                mandatory_depends_on='eval:parent.purchase_type || parent.agricultural_goods',
+                # tax_type (Tax Free / Taxable) only applies to a Purchase Act
+                # (5% withholding). EQF / Import documents don't use it, so it is
+                # mandatory only when act_type == "Purchase Act".
+                mandatory_depends_on='eval:parent.act_type == "Purchase Act"',
                 in_list_view=1,
                 columns=2
             ),