diff --git a/BizHawk.Client.Common/movie/bk2/Bk2Movie.InputLog.cs b/BizHawk.Client.Common/movie/bk2/Bk2Movie.InputLog.cs
index 99425ac9ed..a7e591b2e8 100644
--- a/BizHawk.Client.Common/movie/bk2/Bk2Movie.InputLog.cs
+++ b/BizHawk.Client.Common/movie/bk2/Bk2Movie.InputLog.cs
@@ -299,8 +299,9 @@ namespace BizHawk.Client.Common
 			var lg = new Bk2LogEntryGenerator(LogKey);
 			lg.SetSource(Global.MovieOutputHardpoint);
 
-			var sb = new StringBuilder();
+			var sb = new StringBuilder();			
 			sb.AppendLine(lg.GenerateLogKey());
+			sb.EnsureCapacity(sb.Capacity + _log.Count);
 			foreach (var record in _log)
 			{
 				sb.AppendLine(record);