diff --git a/deployment/hasura/migrations/Aerie/35_activity_directive_anchor_index/down.sql b/deployment/hasura/migrations/Aerie/35_activity_directive_anchor_index/down.sql
new file mode 100644
index 0000000000..8efd172ad6
--- /dev/null
+++ b/deployment/hasura/migrations/Aerie/35_activity_directive_anchor_index/down.sql
@@ -0,0 +1,23 @@
+create or replace function merlin.get_dependent_activities(_activity_id int, _plan_id int)
+  returns table(activity_id int, total_offset interval)
+  stable
+  language plpgsql as $$
+begin
+  return query
+  with recursive d_activities(activity_id, anchor_id, anchored_to_start, start_offset, total_offset) as (
+      select ad.id, ad.anchor_id, ad.anchored_to_start, ad.start_offset, ad.start_offset
+      from merlin.activity_directive ad
+      where (ad.anchor_id, ad.plan_id) = (_activity_id, _plan_id)
+    union
+      select ad.id, ad.anchor_id, ad.anchored_to_start, ad.start_offset, da.total_offset + ad.start_offset
+      from merlin.activity_directive ad, d_activities da
+      where (ad.anchor_id, ad.plan_id) = (da.activity_id, _plan_id)
+        and ad.anchored_to_start
+  ) select da.activity_id, da.total_offset
+  from d_activities da;
+end;
+$$;
+
+drop index if exists merlin.activity_directive_anchor_id_index;
+
+call migrations.mark_migration_rolled_back(35);
diff --git a/deployment/hasura/migrations/Aerie/35_activity_directive_anchor_index/up.sql b/deployment/hasura/migrations/Aerie/35_activity_directive_anchor_index/up.sql
new file mode 100644
index 0000000000..d28a3dcd41
--- /dev/null
+++ b/deployment/hasura/migrations/Aerie/35_activity_directive_anchor_index/up.sql
@@ -0,0 +1,24 @@
+-- Used by merlin.get_dependent_activities (called per row from validate_anchors_insert_trigger).
+create index activity_directive_anchor_id_index
+  on merlin.activity_directive (anchor_id, plan_id);
+
+-- `language sql` (not plpgsql) so the planner can inline this into the calling
+-- query and pick the index above. The plpgsql wrapper was opaque to the planner.
+create or replace function merlin.get_dependent_activities(_activity_id int, _plan_id int)
+  returns table(activity_id int, total_offset interval)
+  stable
+  language sql as $$
+  with recursive d_activities(activity_id, anchor_id, anchored_to_start, start_offset, total_offset) as (
+      select ad.id, ad.anchor_id, ad.anchored_to_start, ad.start_offset, ad.start_offset
+      from merlin.activity_directive ad
+      where (ad.anchor_id, ad.plan_id) = (_activity_id, _plan_id)
+    union
+      select ad.id, ad.anchor_id, ad.anchored_to_start, ad.start_offset, da.total_offset + ad.start_offset
+      from merlin.activity_directive ad, d_activities da
+      where (ad.anchor_id, ad.plan_id) = (da.activity_id, _plan_id)
+        and ad.anchored_to_start
+  ) select da.activity_id, da.total_offset
+  from d_activities da;
+$$;
+
+call migrations.mark_migration_applied(35);
diff --git a/deployment/postgres-init-db/sql/tables/merlin/activity_directive/activity_directive.sql b/deployment/postgres-init-db/sql/tables/merlin/activity_directive/activity_directive.sql
index 5ddafbb641..cb31084efd 100644
--- a/deployment/postgres-init-db/sql/tables/merlin/activity_directive/activity_directive.sql
+++ b/deployment/postgres-init-db/sql/tables/merlin/activity_directive/activity_directive.sql
@@ -54,6 +54,10 @@ create table merlin.activity_directive (
 
 create index activity_directive_plan_id_index on merlin.activity_directive (plan_id);
 
+-- Used by merlin.get_dependent_activities (called per row from validate_anchors_insert_trigger).
+create index activity_directive_anchor_id_index
+  on merlin.activity_directive (anchor_id, plan_id);
+
 
 comment on table merlin.activity_directive is e''
   'A single activity_directive within a plan.';
diff --git a/deployment/postgres-init-db/sql/tables/merlin/activity_directive/anchor_validation_status.sql b/deployment/postgres-init-db/sql/tables/merlin/activity_directive/anchor_validation_status.sql
index 5484b89736..55e441c840 100644
--- a/deployment/postgres-init-db/sql/tables/merlin/activity_directive/anchor_validation_status.sql
+++ b/deployment/postgres-init-db/sql/tables/merlin/activity_directive/anchor_validation_status.sql
@@ -24,12 +24,13 @@ comment on column merlin.anchor_validation_status.plan_id is e''
 comment on column merlin.anchor_validation_status.reason_invalid is e''
   'If null, the anchor is valid. If not null, this contains a reason why the anchor is invalid.';
 
+-- `language sql` (not plpgsql) so the planner can inline this into the calling
+-- query and pick the (anchor_id, plan_id) index. The plpgsql wrapper was opaque
+-- to the planner and chose a worse plan.
 create function merlin.get_dependent_activities(_activity_id int, _plan_id int)
   returns table(activity_id int, total_offset interval)
   stable
-  language plpgsql as $$
-begin
-  return query
+  language sql as $$
   with recursive d_activities(activity_id, anchor_id, anchored_to_start, start_offset, total_offset) as (
       select ad.id, ad.anchor_id, ad.anchored_to_start, ad.start_offset, ad.start_offset
       from merlin.activity_directive ad
@@ -41,7 +42,6 @@ begin
         and ad.anchored_to_start  -- stop at next end-time anchor
   ) select da.activity_id, da.total_offset
   from d_activities da;
-end;
 $$;
 
 comment on function merlin.get_dependent_activities(_activity_id int, _plan_id int) is e''