diff --git a/lib/beet_round_server/bidding_rounds/bidding_round.ex b/lib/beet_round_server/bidding_rounds/bidding_round.ex
index 6839123..10dd378 100644
--- a/lib/beet_round_server/bidding_rounds/bidding_round.ex
+++ b/lib/beet_round_server/bidding_rounds/bidding_round.ex
@@ -16,5 +16,6 @@ defmodule BeetRoundServer.BiddingRounds.BiddingRound do
     bidding_round
     |> cast(attrs, [:round_number, :stopped])
     |> validate_required([:round_number, :stopped])
+    |> unique_constraint(:round_number)
   end
 end