diff --git a/wfe2/wfe.go b/wfe2/wfe.go
index 0665db0960d..ada0b21686b 100644
--- a/wfe2/wfe.go
+++ b/wfe2/wfe.go
@@ -2054,7 +2054,7 @@ func (wfe *WebFrontEndImpl) KeyRollover(
 
 type orderJSON struct {
 	Status         core.AcmeStatus            `json:"status"`
-	Expires        time.Time                  `json:"expires"`
+	Expires        *time.Time                 `json:"expires,omitempty"`
 	Identifiers    identifier.ACMEIdentifiers `json:"identifiers"`
 	Authorizations []string                   `json:"authorizations"`
 	Finalize       string                     `json:"finalize"`
@@ -2073,12 +2073,16 @@ func (wfe *WebFrontEndImpl) orderToOrderJSON(request *http.Request, order *corep
 		fmt.Sprintf("%d", order.RegistrationID), fmt.Sprintf("%d", order.Id))
 	respObj := orderJSON{
 		Status:      core.AcmeStatus(order.Status),
-		Expires:     order.Expires.AsTime(),
 		Identifiers: identifier.FromProtoSlice(order.Identifiers),
 		Finalize:    finalizeURL,
 		Profile:     order.CertificateProfileName,
 		Replaces:    order.Replaces,
 	}
+	// Omit expires when unset rather than serialize a zero-value timestamp.
+	if !core.IsAnyNilOrZero(order.Expires) {
+		expires := order.Expires.AsTime()
+		respObj.Expires = &expires
+	}
 	// If there is an order error, prefix its type with the V2 namespace
 	if order.Error != nil {
 		prob, err := bgrpc.PBToProblemDetails(order.Error)
diff --git a/wfe2/wfe_test.go b/wfe2/wfe_test.go
index ab0e4b92b46..441f4dc0e1c 100644
--- a/wfe2/wfe_test.go
+++ b/wfe2/wfe_test.go
@@ -3812,6 +3812,32 @@ func TestOrderToOrderJSONV2Authorizations(t *testing.T) {
 	})
 }
 
+func TestOrderToOrderJSONExpires(t *testing.T) {
+	wfe, _, _ := setupWFE(t)
+
+	expires := time.Date(2024, 1, 2, 3, 4, 5, 0, time.UTC)
+	withExpiry := wfe.orderToOrderJSON(&http.Request{}, &corepb.Order{
+		Id:             1,
+		RegistrationID: 1,
+		Identifiers:    []*corepb.Identifier{identifier.NewDNS("a").ToProto()},
+		Status:         string(core.StatusPending),
+		Expires:        timestamppb.New(expires),
+	})
+	got, err := json.Marshal(withExpiry)
+	test.AssertNotError(t, err, "marshaling order with an expiry")
+	test.AssertContains(t, string(got), `"expires":"2024-01-02T03:04:05Z"`)
+
+	withoutExpiry := wfe.orderToOrderJSON(&http.Request{}, &corepb.Order{
+		Id:             1,
+		RegistrationID: 1,
+		Identifiers:    []*corepb.Identifier{identifier.NewDNS("a").ToProto()},
+		Status:         string(core.StatusPending),
+	})
+	got, err = json.Marshal(withoutExpiry)
+	test.AssertNotError(t, err, "marshaling order without an expiry")
+	test.AssertNotContains(t, string(got), "expires")
+}
+
 func TestAccountMarshaling(t *testing.T) {
 	acct := &core.Registration{
 		ID:        1987,