diff --git a/lib/model/activity.js b/lib/model/activity.js
index <HASH>..<HASH> 100644
--- a/lib/model/activity.js
+++ b/lib/model/activity.js
@@ -570,6 +570,9 @@ Activity.prototype.applyJoin = function(callback) {
 	},
 	function(err, post) {
 	    if (err) throw err;
+            if (!post) {
+		throw new AppError("Can't join group: no access");
+	    }
 	    post.checkRecipient(act.actor, this);
 	},
 	function(err, isRecipient) {
Handle the case where there is no post activity for a group