diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Order.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Order.java
index 4e22c3d4..52faac39 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Order.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Order.java
@@ -114,12 +114,17 @@ public class Order extends AcmeJsonResource {
     }
 
     /**
-     * Gets the {@link Certificate} if it is available.
+     * Gets the {@link Certificate}.
+     *
+     * @throws IllegalStateException
+     *         if the order is not ready yet. You must finalize the order first, and wait
+     *         for the status to become {@link Status#VALID}.
      */
-    public Optional<Certificate> getCertificate() {
+    public Certificate getCertificate() {
         return getJSON().get("certificate")
-                    .map(Value::asURL)
-                    .map(getLogin()::bindCertificate);
+                .map(Value::asURL)
+                .map(getLogin()::bindCertificate)
+                .orElseThrow(() -> new IllegalStateException("Order is not completed"));
     }
 
     /**
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java
index 0631bf1f..a35ae955 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/OrderTest.java
@@ -79,7 +79,7 @@ public class OrderTest {
                     .isEqualTo("2016-01-01T00:00:00Z");
             softly.assertThat(order.getNotAfter().orElseThrow())
                     .isEqualTo("2016-01-08T00:00:00Z");
-            softly.assertThat(order.getCertificate().orElseThrow().getLocation())
+            softly.assertThat(order.getCertificate().getLocation())
                     .isEqualTo(url("https://example.com/acme/cert/1234"));
             softly.assertThat(order.getFinalizeLocation()).isEqualTo(finalizeUrl);
 
@@ -141,13 +141,13 @@ public class OrderTest {
         try (var softly = new AutoCloseableSoftAssertions()) {
             // Lazy loading
             softly.assertThat(requestWasSent).isFalse();
-            softly.assertThat(order.getCertificate().orElseThrow().getLocation())
+            softly.assertThat(order.getCertificate().getLocation())
                     .isEqualTo(url("https://example.com/acme/cert/1234"));
             softly.assertThat(requestWasSent).isTrue();
 
             // Subsequent queries do not trigger another load
             requestWasSent.set(false);
-            softly.assertThat(order.getCertificate().orElseThrow().getLocation())
+            softly.assertThat(order.getCertificate().getLocation())
                     .isEqualTo(url("https://example.com/acme/cert/1234"));
             softly.assertThat(order.getStatus()).isEqualTo(Status.PENDING);
             softly.assertThat(order.getExpires().orElseThrow()).isEqualTo("2015-03-01T14:09:00Z");
@@ -210,7 +210,7 @@ public class OrderTest {
                     .isEqualTo("2016-01-01T00:00:00Z");
             softly.assertThat(order.getNotAfter().orElseThrow())
                     .isEqualTo("2016-01-08T00:00:00Z");
-            softly.assertThat(order.getCertificate().orElseThrow().getLocation())
+            softly.assertThat(order.getCertificate().getLocation())
                     .isEqualTo(url("https://example.com/acme/cert/1234"));
             softly.assertThat(order.getAutoRenewalCertificate()).isEmpty();
             softly.assertThat(order.getFinalizeLocation()).isEqualTo(finalizeUrl);
diff --git a/acme4j-example/src/main/java/org/shredzone/acme4j/example/ClientTest.java b/acme4j-example/src/main/java/org/shredzone/acme4j/example/ClientTest.java
index 2efcfa75..5574c691 100644
--- a/acme4j-example/src/main/java/org/shredzone/acme4j/example/ClientTest.java
+++ b/acme4j-example/src/main/java/org/shredzone/acme4j/example/ClientTest.java
@@ -142,7 +142,7 @@ public class ClientTest {
         }
 
         // Get the certificate
-        Certificate certificate = order.getCertificate().orElseThrow();
+        Certificate certificate = order.getCertificate();
 
         LOG.info("Success! The certificate for domains {} has been generated!", domains);
         LOG.info("Certificate URL: {}", certificate.getLocation());
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java
index c585e59b..8fa97d24 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/boulder/OrderHttpIT.java
@@ -23,7 +23,6 @@ import java.security.KeyPair;
 import org.junit.jupiter.api.Test;
 import org.shredzone.acme4j.AccountBuilder;
 import org.shredzone.acme4j.Authorization;
-import org.shredzone.acme4j.Certificate;
 import org.shredzone.acme4j.Order;
 import org.shredzone.acme4j.Session;
 import org.shredzone.acme4j.Status;
@@ -93,9 +92,7 @@ public class OrderHttpIT {
             .conditionEvaluationListener(cond -> updateOrder(order))
             .untilAsserted(() -> assertThat(order.getStatus()).isNotIn(Status.PENDING, Status.PROCESSING));
 
-        var cert = order.getCertificate()
-                .map(Certificate::getCertificate)
-                .orElseThrow();
+        var cert = order.getCertificate().getCertificate();
         assertThat(cert.getNotAfter()).isNotNull();
         assertThat(cert.getNotBefore()).isNotNull();
         assertThat(cert.getSubjectX500Principal().getName()).contains("CN=" + TEST_DOMAIN);
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java
index 55fd6081..f9b44a01 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderIT.java
@@ -195,7 +195,7 @@ public class OrderIT extends PebbleITBase {
 
         assertThat(order.getStatus()).isEqualTo(Status.VALID);
 
-        var certificate = order.getCertificate().orElseThrow();
+        var certificate = order.getCertificate();
         var cert = certificate.getCertificate();
         assertThat(cert).isNotNull();
         assertThat(cert.getNotBefore().toInstant()).isEqualTo(notBefore);
diff --git a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java
index 2286ca22..8fd2f972 100644
--- a/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java
+++ b/acme4j-it/src/test/java/org/shredzone/acme4j/it/pebble/OrderWildcardIT.java
@@ -25,7 +25,6 @@ import java.time.temporal.ChronoUnit;
 import org.bouncycastle.asn1.x509.GeneralName;
 import org.junit.jupiter.api.Test;
 import org.shredzone.acme4j.AccountBuilder;
-import org.shredzone.acme4j.Certificate;
 import org.shredzone.acme4j.Session;
 import org.shredzone.acme4j.Status;
 import org.shredzone.acme4j.challenge.Dns01Challenge;
@@ -112,9 +111,7 @@ public class OrderWildcardIT extends PebbleITBase {
                     order.getStatus()).isNotIn(Status.PENDING, Status.PROCESSING));
 
 
-        var cert = order.getCertificate()
-                .map(Certificate::getCertificate)
-                .orElseThrow();
+        var cert = order.getCertificate().getCertificate();
         assertThat(cert).isNotNull();
         assertThat(cert.getNotAfter()).isNotEqualTo(notBefore);
         assertThat(cert.getNotBefore()).isNotEqualTo(notAfter);