diff --git a/osu.Game/Database/OsuDbContext.cs b/osu.Game/Database/OsuDbContext.cs
index 453e0271e2..7ffde8bf0e 100644
--- a/osu.Game/Database/OsuDbContext.cs
+++ b/osu.Game/Database/OsuDbContext.cs
@@ -119,6 +119,8 @@ namespace osu.Game.Database
             modelBuilder.Entity<RulesetInfo>().HasIndex(b => b.ShortName).IsUnique();
 
             modelBuilder.Entity<BeatmapInfo>().HasOne(b => b.BaseDifficulty);
+
+            modelBuilder.Entity<ScoreInfo>().HasIndex(b => b.OnlineScoreID).IsUnique();
         }
 
         private class OsuDbLoggerFactory : ILoggerFactory
diff --git a/osu.Game/Scoring/ScoreInfo.cs b/osu.Game/Scoring/ScoreInfo.cs
index 9c4d196a04..056bec1d8c 100644
--- a/osu.Game/Scoring/ScoreInfo.cs
+++ b/osu.Game/Scoring/ScoreInfo.cs
@@ -67,7 +67,7 @@ namespace osu.Game.Scoring
 
         public BeatmapInfo BeatmapInfo;
 
-        public long OnlineScoreID;
+        public long? OnlineScoreID { get; set; }
 
         public DateTimeOffset Date;