1 files changed, 1 insertions, 0 deletions
diff --git a/src/DotNetOpenAuth.OAuth2.AuthorizationServer/OAuth2/AuthorizationServerAccessToken.cs b/src/DotNetOpenAuth.OAuth2.AuthorizationServer/OAuth2/AuthorizationServerAccessToken.cs
index c577a0a..a127166 100644
--- a/src/DotNetOpenAuth.OAuth2.AuthorizationServer/OAuth2/AuthorizationServerAccessToken.cs
+++ b/src/DotNetOpenAuth.OAuth2.AuthorizationServer/OAuth2/AuthorizationServerAccessToken.cs
@@ -45,6 +45,7 @@ namespace DotNetOpenAuth.OAuth2 {
 		/// </summary>
 		/// <returns>A non-empty string.</returns>
 		protected internal override string Serialize() {
+			ErrorUtilities.VerifyHost(this.AccessTokenSigningKey != null, AuthServerStrings.AccessTokenSigningKeyMissing);
 			var formatter = CreateFormatter(this.AccessTokenSigningKey, this.ResourceServerEncryptionKey);
 			return formatter.Serialize(this);
 		}