diff --git a/pylabrobot/liquid_handling/liquid_handler.py b/pylabrobot/liquid_handling/liquid_handler.py
index 0224803212..29971517a2 100644
--- a/pylabrobot/liquid_handling/liquid_handler.py
+++ b/pylabrobot/liquid_handling/liquid_handler.py
@@ -1813,7 +1813,7 @@ async def drop_resource(
     )
 
     # get the location of the destination
-    if isinstance(destination, ResourceStack):
+    if isinstance(destination, ResourceStack) and not isinstance(resource, Lid):
       assert (
         destination.direction == "z"
       ), "Only ResourceStacks with direction 'z' are currently supported"
@@ -1835,13 +1835,26 @@ async def drop_resource(
         resource.rotated(z=resource_rotation_wrt_destination_wrt_local)
       ).rotated(destination.get_absolute_rotation())
       to_location = destination.get_absolute_location() + adjusted_plate_anchor
-    elif isinstance(destination, Plate) and isinstance(resource, Lid):
+    # Automatically assign lid to plate as child when dropping a lid to a plate (on or off resource stack)
+    elif isinstance(destination, (Plate, ResourceStack)) and isinstance(resource, Lid):
       lid = resource
-      plate_location = destination.get_absolute_location()
-      child_wrt_parent = destination.get_lid_location(
-        lid.rotated(z=resource_rotation_wrt_destination_wrt_local)
-      ).rotated(destination.get_absolute_rotation())
-      to_location = plate_location + child_wrt_parent
+      if isinstance(destination, ResourceStack):
+        if destination.direction != "z":
+          raise ValueError("Only ResourceStacks with direction 'z' are currently supported")
+        if len(destination.children) == 0:
+          to_location = destination.get_absolute_location(z="top")
+        else:
+          top_item = destination.get_top_item()
+          if isinstance(top_item, Plate):
+            destination = top_item
+          else:
+            to_location = destination.get_absolute_location(z="top")
+      if isinstance(destination, Plate):
+        plate_location = destination.get_absolute_location()
+        child_wrt_parent = destination.get_lid_location(
+          lid.rotated(z=resource_rotation_wrt_destination_wrt_local)
+        ).rotated(destination.get_absolute_rotation())
+        to_location = plate_location + child_wrt_parent
     else:
       to_location = destination.get_absolute_location()
 
diff --git a/pylabrobot/resources/carrier.py b/pylabrobot/resources/carrier.py
index 6eabb1de3c..122c5ed218 100644
--- a/pylabrobot/resources/carrier.py
+++ b/pylabrobot/resources/carrier.py
@@ -234,8 +234,25 @@ def _update_resource_stack_location(self, resource: Resource):
     Args:
       resource: The Resource on the ResourceStack tht was assigned.
     """
-    resource_stack = resource.parent
-    assert isinstance(resource_stack, ResourceStack)
+
+    if isinstance(resource, Lid):
+      lid_parent = resource.parent
+      if lid_parent is None:
+        raise ValueError("Lid has no parent. ResourceStack not found for Lid")
+      if isinstance(lid_parent, ResourceStack):
+        resource_stack = lid_parent
+      elif isinstance(lid_parent.parent, ResourceStack):
+        resource_stack = lid_parent.parent
+      else:
+        raise ValueError("ResourceStack not found for Lid")
+    else:
+      if resource.parent is None:
+        raise ValueError("ResourceStack not found for resource")
+      if not isinstance(resource.parent, ResourceStack):
+        raise TypeError(
+          f"Resource {resource} is not a child of a ResourceStack, but of {type(resource.parent)}"
+        )
+      resource_stack = resource.parent
     if resource_stack.children[0] == resource:
       resource_stack.location = self.get_default_child_location(resource)