diff --git a/app/controllers/events_controller.rb b/app/controllers/events_controller.rb
index 8649eb559..6506354de 100644
--- a/app/controllers/events_controller.rb
+++ b/app/controllers/events_controller.rb
@@ -44,7 +44,7 @@ def rsvp
     ticket = Services::Ticket.new(request, params)
     member = Member.find_by(email: ticket.email)
     invitation = member.invitations.where(event: @event, role: 'Student').first
-    invitation ||= Invitation.create(event: @event, member: member, role: 'Student')
+    invitation ||= Invitation.create_or_find_by(event: @event, member: member, role: 'Student')
 
     invitation.update(attending: true)
     head :ok
@@ -63,7 +63,7 @@ def latest_model_updated
 
   def find_invitation_and_redirect_to_event(role)
     set_event
-    @invitation = Invitation.find_or_create_by(event: @event, member: current_user, role: role)
+    @invitation = Invitation.create_or_find_by(event: @event, member: current_user, role: role)
     redirect_to event_invitation_path(@event, @invitation)
   end
 
diff --git a/app/controllers/workshops_controller.rb b/app/controllers/workshops_controller.rb
index afe29a49e..20753a58c 100644
--- a/app/controllers/workshops_controller.rb
+++ b/app/controllers/workshops_controller.rb
@@ -44,7 +44,7 @@ def find_attending_invitation(workshop, user)
   end
 
   def find_or_create_invitation(workshop, user, role)
-    WorkshopInvitation.find_or_create_by(workshop: workshop,
+    WorkshopInvitation.create_or_find_by(workshop: workshop,
                                          member: user,
                                          role: role)
   end
diff --git a/db/migrate/20260731104506_add_unique_indexes_for_unique_validations.rb b/db/migrate/20260731104506_add_unique_indexes_for_unique_validations.rb
index f4c82f7c0..f925a262e 100644
--- a/db/migrate/20260731104506_add_unique_indexes_for_unique_validations.rb
+++ b/db/migrate/20260731104506_add_unique_indexes_for_unique_validations.rb
@@ -1,15 +1,51 @@
 class AddUniqueIndexesForUniqueValidations < ActiveRecord::Migration[8.1]
   disable_ddl_transaction!
 
-  def change
-    add_index :auth_services, %i[uid provider], unique: true, algorithm: :concurrently
-    add_index :chapters, :name, unique: true, algorithm: :concurrently
-    add_index :chapters, :email, unique: true, algorithm: :concurrently
-    add_index :feedback_requests, %i[member_id workshop_id], unique: true, algorithm: :concurrently
-    add_index :feedback_requests, :token, unique: true, algorithm: :concurrently
-    add_index :invitations, %i[member_id event_id role], unique: true, algorithm: :concurrently
-    add_index :meeting_invitations, %i[member_id meeting_id], unique: true, algorithm: :concurrently
-    add_index :workshop_invitations, %i[member_id workshop_id role], unique: true, algorithm: :concurrently
-    add_index :workshop_sponsors, %i[sponsor_id workshop_id], unique: true, algorithm: :concurrently
+  def up
+    # Production already had duplicate rows (a Rails uniqueness validation is not
+    # atomic, so concurrent double-creates slipped through) that these unique
+    # indexes would reject. Clean them first; this is a no-op on clean data.
+    dedupe! :invitations, %i[member_id event_id role]
+    dedupe! :workshop_invitations, %i[member_id workshop_id role]
+    dedupe! :meeting_invitations, %i[member_id meeting_id]
+
+    # if_not_exists: prod's release phase aborted midway on first run, leaving 5
+    # of these indexes already created. Keep this migration safe to re-run.
+    add_index :auth_services, %i[uid provider], unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :chapters, :name, unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :chapters, :email, unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :feedback_requests, %i[member_id workshop_id], unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :feedback_requests, :token, unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :invitations, %i[member_id event_id role], unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :meeting_invitations, %i[member_id meeting_id], unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :workshop_invitations, %i[member_id workshop_id role], unique: true, algorithm: :concurrently, if_not_exists: true
+    add_index :workshop_sponsors, %i[sponsor_id workshop_id], unique: true, algorithm: :concurrently, if_not_exists: true
+  end
+
+  def down
+    remove_index :auth_services, %i[uid provider]
+    remove_index :chapters, :name
+    remove_index :chapters, :email
+    remove_index :feedback_requests, %i[member_id workshop_id]
+    remove_index :feedback_requests, :token
+    remove_index :invitations, %i[member_id event_id role]
+    remove_index :meeting_invitations, %i[member_id meeting_id]
+    remove_index :workshop_invitations, %i[member_id workshop_id role]
+    remove_index :workshop_sponsors, %i[sponsor_id workshop_id]
+  end
+
+  private
+
+  # Keep the newest row per (columns) group, tie-breaking by lowest id, so a real
+  # RSVP/verification update on any one row (e.g. attending=true) is never dropped.
+  def dedupe!(table, columns)
+    join = columns.map { |c| "i.#{c} = k.#{c}" }.join(' AND ')
+    safety_assured do
+      execute <<~SQL
+        DELETE FROM #{table} AS i
+        USING #{table} AS k
+        WHERE #{join} AND (k.updated_at, -k.id) > (i.updated_at, -i.id)
+      SQL
+    end
   end
 end