diff --git a/src/DotRecast.Detour/Io/DtMeshSetReader.cs b/src/DotRecast.Detour/Io/DtMeshSetReader.cs
index 26b384e..a02e020 100644
--- a/src/DotRecast.Detour/Io/DtMeshSetReader.cs
+++ b/src/DotRecast.Detour/Io/DtMeshSetReader.cs
@@ -67,7 +67,7 @@ namespace DotRecast.Detour.Io
 
             bool cCompatibility = header.version == NavMeshSetHeader.NAVMESHSET_VERSION;
             DtNavMesh mesh = new DtNavMesh(header.option, header.maxVertsPerPoly);
-            ReadTiles(bb, is32Bit, header, cCompatibility, mesh);
+            ReadTiles(bb, is32Bit, ref header, cCompatibility, mesh);
             return mesh;
         }
 
@@ -104,7 +104,7 @@ namespace DotRecast.Detour.Io
             return header;
         }
 
-        private void ReadTiles(RcByteBuffer bb, bool is32Bit, NavMeshSetHeader header, bool cCompatibility, DtNavMesh mesh)
+        private void ReadTiles(RcByteBuffer bb, bool is32Bit, ref NavMeshSetHeader header, bool cCompatibility, DtNavMesh mesh)
         {
             // Read tiles.
             for (int i = 0; i < header.numTiles; ++i)
diff --git a/src/DotRecast.Detour/Io/NavMeshSetHeader.cs b/src/DotRecast.Detour/Io/NavMeshSetHeader.cs
index 11ba57c..2d7ab1c 100644
--- a/src/DotRecast.Detour/Io/NavMeshSetHeader.cs
+++ b/src/DotRecast.Detour/Io/NavMeshSetHeader.cs
@@ -18,7 +18,7 @@ freely, subject to the following restrictions:
 
 namespace DotRecast.Detour.Io
 {
-    public class NavMeshSetHeader
+    public struct NavMeshSetHeader
     {
         public const int NAVMESHSET_MAGIC = 'M' << 24 | 'S' << 16 | 'E' << 8 | 'T'; // 'MSET';
         public const int NAVMESHSET_VERSION = 1;
@@ -28,7 +28,7 @@ namespace DotRecast.Detour.Io
         public int magic;
         public int version;
         public int numTiles;
-        public DtNavMeshParams option = new DtNavMeshParams();
+        public DtNavMeshParams option;
         public int maxVertsPerPoly;
     }
 }
\ No newline at end of file