diff --git a/launch_ros/launch_ros/actions/node.py b/launch_ros/launch_ros/actions/node.py
index 82764258f..6824d7d57 100644
--- a/launch_ros/launch_ros/actions/node.py
+++ b/launch_ros/launch_ros/actions/node.py
@@ -69,7 +69,7 @@ class Node(ExecuteProcess):
 
     def __init__(
         self, *,
-        executable: Optional[SomeSubstitutionsType] = None,
+        executable: SomeSubstitutionsType,
         package: Optional[SomeSubstitutionsType] = None,
         name: Optional[SomeSubstitutionsType] = None,
         namespace: Optional[SomeSubstitutionsType] = None,
diff --git a/launch_ros/launch_ros/descriptions/composable_node.py b/launch_ros/launch_ros/descriptions/composable_node.py
index 01352c700..c2fa4abc1 100644
--- a/launch_ros/launch_ros/descriptions/composable_node.py
+++ b/launch_ros/launch_ros/descriptions/composable_node.py
@@ -35,7 +35,7 @@ class ComposableNode:
     def __init__(
         self, *,
         package: SomeSubstitutionsType,
-        plugin: Optional[SomeSubstitutionsType] = None,
+        plugin: SomeSubstitutionsType,
         name: Optional[SomeSubstitutionsType] = None,
         namespace: Optional[SomeSubstitutionsType] = None,
         parameters: Optional[SomeParameters] = None,