diff --git a/Octokit/GitHubClient.cs b/Octokit/GitHubClient.cs
index 78106a26..fc8816a7 100644
--- a/Octokit/GitHubClient.cs
+++ b/Octokit/GitHubClient.cs
@@ -128,7 +128,7 @@ namespace Octokit
         public IConnection Connection { get; private set; }
 
         public IAuthorizationsClient Authorization { get; private set; }
-        public IActivitiesClient Activity { get; set; }
+        public IActivitiesClient Activity { get; private set; }
         public IBlobsClient Blob { get; private set; }
         public IIssuesClient Issue { get; private set; }
         public IMiscellaneousClient Miscellaneous { get; private set; }