diff --git a/rclcpp/include/rclcpp/node.hpp b/rclcpp/include/rclcpp/node.hpp
index fcbe525..e19f338 100644
--- a/rclcpp/include/rclcpp/node.hpp
+++ b/rclcpp/include/rclcpp/node.hpp
@@ -85,17 +85,24 @@ public:
     rclcpp::timer::CallbackType callback,
     rclcpp::callback_group::CallbackGroup::SharedPtr group=nullptr);
 
+  typedef rclcpp::callback_group::CallbackGroup CallbackGroup;
+  typedef std::weak_ptr<CallbackGroup> CallbackGroupWeakPtr;
+  typedef std::list<CallbackGroupWeakPtr> CallbackGroupWeakPtrList;
+
 private:
   RCLCPP_DISABLE_COPY(Node);
 
+  bool
+  group_in_node(callback_group::CallbackGroup::SharedPtr &group);
+
   std::string name_;
 
   ros_middleware_interface::NodeHandle node_handle_;
 
   rclcpp::context::Context::SharedPtr context_;
 
-  rclcpp::callback_group::CallbackGroup::SharedPtr default_callback_group_;
-  std::list<std::weak_ptr<rclcpp::callback_group::CallbackGroup>> callback_groups_;
+  CallbackGroup::SharedPtr default_callback_group_;
+  CallbackGroupWeakPtrList callback_groups_;
 
   size_t number_of_subscriptions_;
   size_t number_of_timers_;
diff --git a/rclcpp/include/rclcpp/node_impl.hpp b/rclcpp/include/rclcpp/node_impl.hpp
index c8f69d6..22856df 100644
--- a/rclcpp/include/rclcpp/node_impl.hpp
+++ b/rclcpp/include/rclcpp/node_impl.hpp
@@ -40,7 +40,8 @@ Node::Node(std::string node_name)
 {}
 
 Node::Node(std::string node_name, context::Context::SharedPtr context)
-  : name_(node_name), context_(context), number_of_subscriptions_(0)
+  : name_(node_name), context_(context),
+    number_of_subscriptions_(0), number_of_timers_(0)
 {
   node_handle_ = ::ros_middleware_interface::create_node();
   using rclcpp::callback_group::CallbackGroupType;
@@ -54,7 +55,9 @@ Node::create_callback_group(
 {
   using rclcpp::callback_group::CallbackGroup;
   using rclcpp::callback_group::CallbackGroupType;
-  return CallbackGroup::SharedPtr(new CallbackGroup(group_type));
+  auto group = CallbackGroup::SharedPtr(new CallbackGroup(group_type));
+  callback_groups_.push_back(group);
+  return group;
 }
 
 template<typename MessageT>
@@ -71,6 +74,21 @@ Node::create_publisher(std::string topic_name, size_t queue_size)
   return publisher::Publisher::make_shared(publisher_handle);
 }
 
+bool
+Node::group_in_node(callback_group::CallbackGroup::SharedPtr &group)
+{
+  bool group_belongs_to_this_node = false;
+  for (auto &weak_group : this->callback_groups_)
+  {
+    auto cur_group = weak_group.lock();
+    if (cur_group && cur_group == group)
+    {
+      group_belongs_to_this_node = true;
+    }
+  }
+  return group_belongs_to_this_node;
+}
+
 template<typename MessageT>
 typename subscription::Subscription<MessageT>::SharedPtr
 Node::create_subscription(
@@ -94,6 +112,11 @@ Node::create_subscription(
   auto sub_base_ptr = std::dynamic_pointer_cast<SubscriptionBase>(sub);
   if (group)
   {
+    if (!group_in_node(group))
+    {
+      // TODO: use custom exception
+      throw std::runtime_error("Cannot create timer, group not in node.");
+    }
     group->add_subscription(sub_base_ptr);
   }
   else
@@ -109,9 +132,14 @@ Node::create_wall_timer(std::chrono::nanoseconds period,
                         rclcpp::timer::CallbackType callback,
                         rclcpp::callback_group::CallbackGroup::SharedPtr group)
 {
-  auto timer = rclcpp::timer::WallTimer::make_shared(period);
+  auto timer = rclcpp::timer::WallTimer::make_shared(period, callback);
   if (group)
   {
+    if (!group_in_node(group))
+    {
+      // TODO: use custom exception
+      throw std::runtime_error("Cannot create timer, group not in node.");
+    }
     group->add_timer(timer);
   }
   else