diff --git a/erpnext/crm/doctype/opportunity/opportunity.py b/erpnext/crm/doctype/opportunity/opportunity.py
index ede7271132f..84ac1f4d300 100644
--- a/erpnext/crm/doctype/opportunity/opportunity.py
+++ b/erpnext/crm/doctype/opportunity/opportunity.py
@@ -399,8 +399,8 @@ def set_multiple_status(names: str | list[str], status: str):
 
 
 def auto_close_opportunity():
-	"""auto close the `Replied` Opportunities after 7 days"""
-	auto_close_after_days = frappe.db.get_single_value("CRM Settings", "close_opportunity_after_days") or 15
+	"""Auto close `Replied` Opportunities inactive for the days configured in CRM Settings."""
+	auto_close_after_days = frappe.db.get_single_value("CRM Settings", "close_opportunity_after_days")
 
 	table = frappe.qb.DocType("Opportunity")
 	opportunities = (
diff --git a/erpnext/patches.txt b/erpnext/patches.txt
index 5db549806a3..65687c7c118 100644
--- a/erpnext/patches.txt
+++ b/erpnext/patches.txt
@@ -489,3 +489,4 @@ erpnext.patches.v16_0.submit_existing_product_bundles #1
 erpnext.patches.v16_0.migrate_subscription_generate_invoice_at
 erpnext.patches.v16_0.rename_subscription_billing_period_fields
 erpnext.patches.v16_0.drop_redundant_serial_no_index_from_sabb
+erpnext.patches.v16_0.set_default_close_opportunity_after_days
diff --git a/erpnext/patches/v16_0/set_default_close_opportunity_after_days.py b/erpnext/patches/v16_0/set_default_close_opportunity_after_days.py
new file mode 100644
index 00000000000..736b584e1de
--- /dev/null
+++ b/erpnext/patches/v16_0/set_default_close_opportunity_after_days.py
@@ -0,0 +1,12 @@
+import frappe
+
+
+def execute():
+	"""Backfill the default for CRM Settings.close_opportunity_after_days.
+
+	The auto-close logic used to fall back to 15 days in code. Now that the fallback is removed,
+	existing sites that never set the value (left blank / 0) need it filled in so opportunities
+	keep auto-closing on the same schedule.
+	"""
+	if not frappe.db.get_single_value("CRM Settings", "close_opportunity_after_days"):
+		frappe.db.set_single_value("CRM Settings", "close_opportunity_after_days", 15)