diff --git a/CHANGELOG.md b/CHANGELOG.md
index 43e98a770..b466b2a70 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 - `cbc.CodeMap`: added `Lookup` method that returns the code matching a given key, falling back hierarchically to less specific keys.
 - `pay`: added `MeansKeyCredit` and `MeansKeyDebit` qualifiers, enabling the `card+credit` and `card+debit` payment means. Adapted all addons mapping payment means to extensions to use the two new qualified means.
 - `es-tbai-v1`: added `es-tbai-bi-activity` extension for the Bizkaia activity code (epígrafe) required for individual suppliers.
+- `pt-saft-v1`: added rule to check that advance payment amounts on invoices are no less than 0 as required by the SAF-T spec.
 
 ## [v0.402.0] - 2026-04-30
 
diff --git a/addons/pt/saft/invoices.go b/addons/pt/saft/invoices.go
index 9c49bc034..884c6e00c 100644
--- a/addons/pt/saft/invoices.go
+++ b/addons/pt/saft/invoices.go
@@ -137,6 +137,9 @@ func billInvoiceRules() *rules.Set {
 					rules.Field("date",
 						rules.Assert("08", "cannot be blank", is.Present),
 					),
+					rules.Field("amount",
+						rules.Assert("16", "must be no less than 0", num.ZeroOrPositive),
+					),
 				),
 			),
 		),
diff --git a/addons/pt/saft/invoices_test.go b/addons/pt/saft/invoices_test.go
index d64db1824..bc868d2e7 100644
--- a/addons/pt/saft/invoices_test.go
+++ b/addons/pt/saft/invoices_test.go
@@ -412,6 +412,20 @@ func TestInvoicePaymentValidation(t *testing.T) {
 		assert.ErrorContains(t, rules.Validate(inv), "cannot be blank")
 	})
 
+	t.Run("advance with negative amount", func(t *testing.T) {
+		d := cal.NewDate(2024, 1, 1)
+		inv := calculatedInvoice(t)
+		inv.Payment = &bill.PaymentDetails{
+			Advances: []*pay.Record{
+				{
+					Date:   d,
+					Amount: num.MakeAmount(-50, 0),
+				},
+			},
+		}
+		assert.ErrorContains(t, rules.Validate(inv), "must be no less than 0")
+	})
+
 	t.Run("nil advance", func(t *testing.T) {
 		inv := calculatedInvoice(t)
 		inv.Payment = &bill.PaymentDetails{
diff --git a/data/rules/pt-saft.json b/data/rules/pt-saft.json
index e90202215..ca2743f83 100644
--- a/data/rules/pt-saft.json
+++ b/data/rules/pt-saft.json
@@ -92,6 +92,16 @@
                           "tests": "present"
                         }
                       ]
+                    },
+                    {
+                      "field": "amount",
+                      "assert": [
+                        {
+                          "id": "GOBL-PT-SAFT-BILL-INVOICE-16",
+                          "desc": "must be no less than 0",
+                          "tests": "min 0"
+                        }
+                      ]
                     }
                   ]
                 }