diff --git a/OpenRA.Game/ObjectCreator.cs b/OpenRA.Game/ObjectCreator.cs
index bb9d72d097..e8b6900620 100644
--- a/OpenRA.Game/ObjectCreator.cs
+++ b/OpenRA.Game/ObjectCreator.cs
@@ -55,7 +55,9 @@ namespace OpenRA
 			//   (a) loading duplicate data into the application domain, breaking the world.
 			//   (b) crashing if the assembly has already been loaded.
 			// We can't check the internal name of the assembly, so we'll work off the data instead
-			var hash = CryptoUtil.SHA1Hash(File.ReadAllBytes(resolvedPath));
+			string hash;
+			using (var stream = File.OpenRead(resolvedPath))
+				hash = CryptoUtil.SHA1Hash(stream);
 
 			if (!ResolvedAssemblies.TryGetValue(hash, out var assembly))
 			{
diff --git a/OpenRA.Mods.Cnc/FileSystem/MixFile.cs b/OpenRA.Mods.Cnc/FileSystem/MixFile.cs
index 77e157b0be..54dcb15015 100644
--- a/OpenRA.Mods.Cnc/FileSystem/MixFile.cs
+++ b/OpenRA.Mods.Cnc/FileSystem/MixFile.cs
@@ -68,7 +68,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 			{
 				var classicIndex = new Dictionary<string, PackageEntry>();
 				var crcIndex = new Dictionary<string, PackageEntry>();
-				IEnumerable<string> allPossibleFilenames = globalFilenames;
+				var allPossibleFilenames = new HashSet<string>(globalFilenames);
 
 				// Try and find a local mix database
 				var dbNameClassic = PackageEntry.HashFilename("local mix database.dat", PackageHashType.Classic);
@@ -80,14 +80,15 @@ namespace OpenRA.Mods.Cnc.FileSystem
 						using (var content = GetContent(kv.Value))
 						{
 							var db = new XccLocalDatabase(content);
-							allPossibleFilenames = allPossibleFilenames.Concat(db.Entries);
+							allPossibleFilenames.EnsureCapacity(allPossibleFilenames.Count + db.Entries.Length);
+							allPossibleFilenames.UnionWith(db.Entries);
 						}
 
 						break;
 					}
 				}
 
-				foreach (var filename in allPossibleFilenames.Distinct())
+				foreach (var filename in allPossibleFilenames)
 				{
 					var classicHash = PackageEntry.HashFilename(filename, PackageHashType.Classic);
 					var crcHash = PackageEntry.HashFilename(filename, PackageHashType.CRC32);
@@ -237,7 +238,7 @@ namespace OpenRA.Mods.Cnc.FileSystem
 			if (globalFilenames == null)
 				if (context.TryOpen("global mix database.dat", out var mixDatabase))
 					using (var db = new XccGlobalDatabase(mixDatabase))
-						globalFilenames = db.Entries.Distinct().ToArray();
+						globalFilenames = db.Entries.ToHashSet().ToArray();
 
 			package = new MixFile(s, filename, globalFilenames ?? Array.Empty<string>());
 			return true;