diff --git a/rclcpp/include/rclcpp/executor.hpp b/rclcpp/include/rclcpp/executor.hpp
index 4bf346d7d3..53d58af41c 100644
--- a/rclcpp/include/rclcpp/executor.hpp
+++ b/rclcpp/include/rclcpp/executor.hpp
@@ -284,7 +284,7 @@ class Executor
           }));
     }
     // Use the number of subscriptions to allocate memory in the handles
-    unsigned long number_of_subscriptions = subs.size();
+    size_t number_of_subscriptions = subs.size();
     rmw_subscriptions_t subscriber_handles;
     subscriber_handles.subscriber_count = number_of_subscriptions;
     // TODO(wjwwood): Avoid redundant malloc's
@@ -303,7 +303,7 @@ class Executor
     }
 
     // Use the number of services to allocate memory in the handles
-    unsigned long number_of_services = services.size();
+    size_t number_of_services = services.size();
     rmw_services_t service_handles;
     service_handles.service_count = number_of_services;
     service_handles.services =
@@ -321,7 +321,7 @@ class Executor
     }
 
     // Use the number of clients to allocate memory in the handles
-    unsigned long number_of_clients = clients.size();
+    size_t number_of_clients = clients.size();
     rmw_clients_t client_handles;
     client_handles.client_count = number_of_clients;
     client_handles.clients =
@@ -341,8 +341,7 @@ class Executor
     // Use the number of guard conditions to allocate memory in the handles
     // Add 2 to the number for the ctrl-c guard cond and the executor's
     size_t start_of_timer_guard_conds = 2;
-    unsigned long number_of_guard_conds =
-      timers.size() + start_of_timer_guard_conds;
+    size_t number_of_guard_conds = timers.size() + start_of_timer_guard_conds;
     rmw_guard_conditions_t guard_condition_handles;
     guard_condition_handles.guard_condition_count = number_of_guard_conds;
     guard_condition_handles.guard_conditions =