diff --git a/acme/api/identifier.go b/acme/api/identifier.go
new file mode 100644
index 0000000000..27337ccba8
--- /dev/null
+++ b/acme/api/identifier.go
@@ -0,0 +1,27 @@
+package api
+
+import (
+	"cmp"
+	"slices"
+
+	"github.com/go-acme/lego/v4/acme"
+)
+
+// compareIdentifiers compares 2 slices of [acme.Identifier].
+func compareIdentifiers(a, b []acme.Identifier) int {
+	// Clones slices to avoid modifying original slices.
+	right := slices.Clone(a)
+	left := slices.Clone(b)
+
+	slices.SortStableFunc(right, compareIdentifier)
+	slices.SortStableFunc(left, compareIdentifier)
+
+	return slices.CompareFunc(right, left, compareIdentifier)
+}
+
+func compareIdentifier(right, left acme.Identifier) int {
+	return cmp.Or(
+		cmp.Compare(right.Type, left.Type),
+		cmp.Compare(right.Value, left.Value),
+	)
+}
diff --git a/acme/api/identifier_test.go b/acme/api/identifier_test.go
new file mode 100644
index 0000000000..586a879869
--- /dev/null
+++ b/acme/api/identifier_test.go
@@ -0,0 +1,111 @@
+package api
+
+import (
+	"testing"
+
+	"github.com/go-acme/lego/v4/acme"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_compareIdentifiers(t *testing.T) {
+	testCases := []struct {
+		desc     string
+		a, b     []acme.Identifier
+		expected int
+	}{
+		{
+			desc: "identical identifiers",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			expected: 0,
+		},
+		{
+			desc: "identical identifiers but different order",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "*.example.com"},
+				{Type: "dns", Value: "example.com"},
+			},
+			expected: 0,
+		},
+		{
+			desc: "duplicate identifiers",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "example.com"},
+			},
+			expected: -1,
+		},
+		{
+			desc: "different identifier values",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.org"},
+			},
+			expected: -1,
+		},
+		{
+			desc: "different identifier types",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "ip", Value: "*.example.com"},
+			},
+			expected: -1,
+		},
+		{
+			desc: "different number of identifiers a>b",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+				{Type: "dns", Value: "example.org"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			expected: 1,
+		},
+		{
+			desc: "different number of identifiers b>a",
+			a: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+			},
+			b: []acme.Identifier{
+				{Type: "dns", Value: "example.com"},
+				{Type: "dns", Value: "*.example.com"},
+				{Type: "dns", Value: "example.org"},
+			},
+			expected: -1,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			assert.Equal(t, test.expected, compareIdentifiers(test.a, test.b))
+		})
+	}
+}
diff --git a/acme/api/order.go b/acme/api/order.go
index 4d310e0409..dd42fb4451 100644
--- a/acme/api/order.go
+++ b/acme/api/order.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"slices"
 	"time"
 
 	"github.com/go-acme/lego/v4/acme"
@@ -85,6 +86,21 @@ func (o *OrderService) NewWithOptions(domains []string, opts *OrderOptions) (acm
 		}
 	}
 
+	// The elements of the "authorizations" and "identifiers" arrays are immutable once set.
+	// The server MUST NOT change the contents of either array after they are created.
+	// If a client observes a change in the contents of either array,
+	// then it SHOULD consider the order invalid.
+	// https://www.rfc-editor.org/rfc/rfc8555#section-7.1.3
+	if compareIdentifiers(orderReq.Identifiers, order.Identifiers) != 0 {
+		// Sorts identifiers to avoid error message ambiguities about the order of the identifiers.
+		slices.SortStableFunc(orderReq.Identifiers, compareIdentifier)
+		slices.SortStableFunc(order.Identifiers, compareIdentifier)
+
+		return acme.ExtendedOrder{},
+			fmt.Errorf("order identifiers have been by the ACME server (RFC8555 §7.1.3): %+v != %+v",
+				orderReq.Identifiers, order.Identifiers)
+	}
+
 	return acme.ExtendedOrder{
 		Order:    order,
 		Location: resp.Header.Get("Location"),