diff --git a/tracetools_analysis/tracetools_analysis/data_model/ros.py b/tracetools_analysis/tracetools_analysis/data_model/ros.py
index 45e6fdf..1598b06 100644
--- a/tracetools_analysis/tracetools_analysis/data_model/ros.py
+++ b/tracetools_analysis/tracetools_analysis/data_model/ros.py
@@ -116,7 +116,7 @@ class RosDataModel(DataModel):
     def add_rclcpp_subscription(
         self, subscription_pointer, timestamp, subscription_handle
     ) -> None:
-        self.subscriptions_objects[subscription_pointer] = [timestamp, subscription_handle]
+        self.subscriptions_objects.loc[subscription_pointer] = [timestamp, subscription_handle]
 
     def add_service(
         self, handle, timestamp, node_handle, rmw_handle, service_name