diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java
index 39000ffb..e8ac8956 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java
@@ -188,9 +188,11 @@ public class Authorization extends AcmeResource {
 
             if (rc == HttpURLConnection.HTTP_ACCEPTED) {
                 Date retryAfter = conn.getRetryAfterHeader();
-                throw new AcmeRetryAfterException(
-                                "authorization is not completed yet",
-                                retryAfter);
+                if (retryAfter != null) {
+                    throw new AcmeRetryAfterException(
+                                    "authorization is not completed yet",
+                                    retryAfter);
+                }
             }
         } catch (IOException ex) {
             throw new AcmeNetworkException(ex);
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
index 8283ecd9..b5e117a8 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
@@ -93,9 +93,11 @@ public class Certificate extends AcmeResource {
                 int rc = conn.sendRequest(getLocation());
                 if (rc == HttpURLConnection.HTTP_ACCEPTED) {
                     Date retryAfter = conn.getRetryAfterHeader();
-                    throw new AcmeRetryAfterException(
-                                    "certificate is not available for download yet",
-                                    retryAfter);
+                    if (retryAfter != null) {
+                        throw new AcmeRetryAfterException(
+                                        "certificate is not available for download yet",
+                                        retryAfter);
+                    }
                 }
 
                 if (rc != HttpURLConnection.HTTP_OK) {