diff --git a/src/ACMESharp/Protocol/Resources/ServiceDirectory.cs b/src/ACMESharp/Protocol/Resources/ServiceDirectory.cs
index 0fcb5e4..c8ceab8 100644
--- a/src/ACMESharp/Protocol/Resources/ServiceDirectory.cs
+++ b/src/ACMESharp/Protocol/Resources/ServiceDirectory.cs
@@ -60,6 +60,6 @@ public class DirectoryMeta
         public string[] CaaIdentities { get; set; }
 
         [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
-        public string ExternalAccountRequired { get; set; }
+        public bool? ExternalAccountRequired { get; set; }
     }
 }