diff --git a/http.go b/http.go
index 3a4ad65..af3ae43 100644
--- a/http.go
+++ b/http.go
@@ -219,9 +219,16 @@ func HttpHandleGroupAddClient(response http.ResponseWriter, request *http.Reques
 	}
 
 	usersToAddString := request.FormValue("users")
-	usersToAdd := strings.SplitN(usersToAddString, ",", int(MaxGroupsForClient))
+	var remainingUsersCount = int(MaxClientsInGroup) - len(group.Clients)
+	if remainingUsersCount < 1 {
+		http.Error(response, "max users", http.StatusUnauthorized)
+		return
+	}
+
+	usersToAdd := strings.SplitN(usersToAddString, ",", remainingUsersCount+1)
 	if len(usersToAdd) == 0 {
 		http.Error(response, "no users to add", http.StatusBadRequest)
+		return
 	}
 
 }