diff --git a/app/services/builtin_callouts.rb b/app/services/builtin_callouts.rb
index f34b6e845..0575e1e89 100644
--- a/app/services/builtin_callouts.rb
+++ b/app/services/builtin_callouts.rb
@@ -131,7 +131,7 @@ def initialize(event)
   def seed
     existing_keys = @event.registration_ticket_callouts.builtin.pluck(:builtin_key).to_set
     definitions.reject { |definition| existing_keys.include?(definition[:builtin_key]) }
-               .map { |definition| create(definition) }
+               .filter_map { |definition| create(definition) }
   end
 
   # In-memory counterpart to #seed. Skips keys already present on the loaded
@@ -294,6 +294,12 @@ def create(definition)
     callout = @event.registration_ticket_callouts.create!(attributes_for(definition))
     build_resource_links(callout, definition)
     callout
+  rescue ActiveRecord::RecordNotUnique
+    # A concurrent request seeded this built-in in the window between our existence
+    # check and this insert, so the unique index on [event_id, builtin_key] rejects
+    # the duplicate. Seeding is idempotent, so drop the failed in-memory row and skip.
+    @event.registration_ticket_callouts.reset
+    nil
   end
 
   # In-memory sibling of #create: builds the row (and its resource links) without
diff --git a/spec/services/builtin_callouts_spec.rb b/spec/services/builtin_callouts_spec.rb
index 737161257..59a1fa72f 100644
--- a/spec/services/builtin_callouts_spec.rb
+++ b/spec/services/builtin_callouts_spec.rb
@@ -230,6 +230,29 @@
       expect(faq.hidden).to be(true)
     end
 
+    it "skips a built-in when the DB unique index rejects a concurrent duplicate" do
+      event = create(:event, cost_cents: 0)
+      service = described_class.new(event)
+
+      # Simulate the concurrency window: the in-memory existence + uniqueness
+      # checks pass, but the unique index on [event_id, builtin_key] rejects the
+      # insert because a concurrent request committed the same row first. Fire it
+      # for Handouts, mirroring the Honeybadger report.
+      original_create = event.registration_ticket_callouts.method(:create!)
+      allow(event.registration_ticket_callouts).to receive(:create!) do |attrs|
+        raise ActiveRecord::RecordNotUnique, "Duplicate entry" if attrs[:builtin_key] == "handouts"
+        original_create.call(attrs)
+      end
+
+      expect { service.seed }.not_to raise_error
+
+      keys = event.registration_ticket_callouts.builtin.pluck(:builtin_key)
+      expect(keys).to contain_exactly(
+        "payment", "certificate", "scholarship", "ce_hours", "art_supplies",
+        "videoconference", "faq"
+      )
+    end
+
     it "appends the built-in callouts after existing custom ones" do
       event = create(:event)
       custom = create(:registration_ticket_callout, event:, title: "Parking")