diff --git a/src/DotRecast.Core/DotRecast.Core.csproj b/src/DotRecast.Core/DotRecast.Core.csproj
index 149d35d..eff52c8 100644
--- a/src/DotRecast.Core/DotRecast.Core.csproj
+++ b/src/DotRecast.Core/DotRecast.Core.csproj
@@ -5,7 +5,6 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="System.Collections.Immutable" Version="7.0.0" />
         <PackageReference Include="System.Text.Json" Version="7.0.3" />
     </ItemGroup>
 
diff --git a/src/DotRecast.Core/RcImmutableArray.Enumerable.cs b/src/DotRecast.Core/RcImmutableArray.Enumerable.cs
new file mode 100644
index 0000000..e3b4769
--- /dev/null
+++ b/src/DotRecast.Core/RcImmutableArray.Enumerable.cs
@@ -0,0 +1,83 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace DotRecast.Core
+{
+    public readonly partial struct RcImmutableArray<T>
+    {
+        public IEnumerator<T> GetEnumerator()
+        {
+            return EnumeratorObject.Create(_array);
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return EnumeratorObject.Create(_array);
+        }
+
+        private sealed class EnumeratorObject : IEnumerator<T>
+        {
+            private static readonly IEnumerator<T> EmptyEnumerator = Create(Empty._array!);
+            private readonly T[] _array;
+            private int _index;
+
+            internal static IEnumerator<T> Create(T[] array)
+            {
+                if (array.Length != 0)
+                {
+                    return new EnumeratorObject(array);
+                }
+                else
+                {
+                    return EmptyEnumerator;
+                }
+            }
+
+
+            private EnumeratorObject(T[] array)
+            {
+                _index = -1;
+                _array = array;
+            }
+
+            public T Current
+            {
+                get
+                {
+                    if (unchecked((uint)_index) < (uint)_array.Length)
+                    {
+                        return _array[_index];
+                    }
+
+                    throw new InvalidOperationException();
+                }
+            }
+
+            object IEnumerator.Current => this.Current;
+
+            public void Dispose()
+            {
+            }
+
+            public bool MoveNext()
+            {
+                int newIndex = _index + 1;
+                int length = _array.Length;
+
+                if ((uint)newIndex <= (uint)length)
+                {
+                    _index = newIndex;
+                    return (uint)newIndex < (uint)length;
+                }
+
+                return false;
+            }
+
+            void IEnumerator.Reset()
+            {
+                _index = -1;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/DotRecast.Core/RcImmutableArray.Listable.cs b/src/DotRecast.Core/RcImmutableArray.Listable.cs
new file mode 100644
index 0000000..b485193
--- /dev/null
+++ b/src/DotRecast.Core/RcImmutableArray.Listable.cs
@@ -0,0 +1,69 @@
+using System;
+using System.Collections.Generic;
+
+namespace DotRecast.Core
+{
+    public readonly partial struct RcImmutableArray<T> : IList<T>
+    {
+        public int Count => Length;
+        public bool IsReadOnly => true;
+
+        T IList<T>.this[int index]
+        {
+            get
+            {
+                var self = this;
+                return self[index];
+            }
+            set => throw new NotSupportedException();
+        }
+
+
+        public int IndexOf(T item)
+        {
+            for (int i = 0; i < Count; ++i)
+            {
+                if (_array![i].Equals(item))
+                    return i;
+            }
+
+            return -1;
+        }
+
+        public bool Contains(T item)
+        {
+            return IndexOf(item) >= 0;
+        }
+
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            var self = this;
+            Array.Copy(self._array!, 0, array, arrayIndex, self.Length);
+        }
+
+        public void Add(T item)
+        {
+            throw new NotSupportedException();
+        }
+
+        public void Clear()
+        {
+            throw new NotSupportedException();
+        }
+
+        public bool Remove(T item)
+        {
+            throw new NotSupportedException();
+        }
+
+        public void Insert(int index, T item)
+        {
+            throw new NotSupportedException();
+        }
+
+        public void RemoveAt(int index)
+        {
+            throw new NotSupportedException();
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/DotRecast.Core/RcImmutableArray.Minimal.cs b/src/DotRecast.Core/RcImmutableArray.Minimal.cs
new file mode 100644
index 0000000..4306936
--- /dev/null
+++ b/src/DotRecast.Core/RcImmutableArray.Minimal.cs
@@ -0,0 +1,19 @@
+namespace DotRecast.Core
+{
+    public readonly partial struct RcImmutableArray<T>
+    {
+#pragma warning disable CA1825
+        public static readonly RcImmutableArray<T> Empty = new RcImmutableArray<T>(new T[0]);
+#pragma warning restore CA1825
+
+        private readonly T[] _array;
+
+        internal RcImmutableArray(T[] items)
+        {
+            _array = items;
+        }
+
+        public T this[int index] => _array![index];
+        public int Length => _array!.Length;
+    }
+}
\ No newline at end of file
diff --git a/src/DotRecast.Core/RcImmutableArray.cs b/src/DotRecast.Core/RcImmutableArray.cs
new file mode 100644
index 0000000..f6c1bc6
--- /dev/null
+++ b/src/DotRecast.Core/RcImmutableArray.cs
@@ -0,0 +1,48 @@
+using System;
+
+namespace DotRecast.Core
+{
+    public static class RcImmutableArray
+    {
+        public static RcImmutableArray<T> Create<T>()
+        {
+            return RcImmutableArray<T>.Empty;
+        }
+
+        public static RcImmutableArray<T> Create<T>(T item1)
+        {
+            T[] array = new[] { item1 };
+            return new RcImmutableArray<T>(array);
+        }
+
+        public static RcImmutableArray<T> Create<T>(T item1, T item2)
+        {
+            T[] array = new[] { item1, item2 };
+            return new RcImmutableArray<T>(array);
+        }
+
+        public static RcImmutableArray<T> Create<T>(T item1, T item2, T item3)
+        {
+            T[] array = new[] { item1, item2, item3 };
+            return new RcImmutableArray<T>(array);
+        }
+
+        public static RcImmutableArray<T> Create<T>(T item1, T item2, T item3, T item4)
+        {
+            T[] array = new[] { item1, item2, item3, item4 };
+            return new RcImmutableArray<T>(array);
+        }
+
+        public static RcImmutableArray<T> Create<T>(params T[] items)
+        {
+            if (items == null || items.Length == 0)
+            {
+                return RcImmutableArray<T>.Empty;
+            }
+
+            var tmp = new T[items.Length];
+            Array.Copy(items, tmp, items.Length);
+            return new RcImmutableArray<T>(tmp);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/DotRecast.Detour.Dynamic/DynamicTile.cs b/src/DotRecast.Detour.Dynamic/DynamicTile.cs
index 8ad460e..f315027 100644
--- a/src/DotRecast.Detour.Dynamic/DynamicTile.cs
+++ b/src/DotRecast.Detour.Dynamic/DynamicTile.cs
@@ -19,7 +19,7 @@ freely, subject to the following restrictions:
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
-using System.Collections.Immutable;
+using System.Collections.ObjectModel;
 using System.Linq;
 using DotRecast.Core;
 using DotRecast.Detour.Dynamic.Colliders;
@@ -60,8 +60,14 @@ namespace DotRecast.Detour.Dynamic
 
         private RcHeightfield BuildHeightfield(DynamicNavMeshConfig config, RcTelemetry telemetry)
         {
-            ICollection<long> rasterizedColliders = checkpoint != null ? checkpoint.colliders : ImmutableHashSet<long>.Empty;
-            RcHeightfield heightfield = checkpoint != null ? checkpoint.heightfield : voxelTile.Heightfield();
+            ICollection<long> rasterizedColliders = checkpoint != null
+                ? checkpoint.colliders as ICollection<long>
+                : RcImmutableArray<long>.Empty;
+
+            RcHeightfield heightfield = checkpoint != null
+                ? checkpoint.heightfield
+                : voxelTile.Heightfield();
+
             foreach (var (cid, c) in colliders)
             {
                 if (!rasterizedColliders.Contains(cid))
diff --git a/src/DotRecast.Detour/DtNavMeshQuery.cs b/src/DotRecast.Detour/DtNavMeshQuery.cs
index 9f3f9d7..dc27feb 100644
--- a/src/DotRecast.Detour/DtNavMeshQuery.cs
+++ b/src/DotRecast.Detour/DtNavMeshQuery.cs
@@ -20,8 +20,6 @@ freely, subject to the following restrictions:
 
 using System;
 using System.Collections.Generic;
-using System.Collections.Immutable;
-using System.Numerics;
 using DotRecast.Core;
 
 namespace DotRecast.Detour
@@ -725,7 +723,7 @@ namespace DotRecast.Detour
         {
             if (!RcVec3f.IsFinite(center) || !RcVec3f.IsFinite(halfExtents))
             {
-                return ImmutableArray<DtMeshTile>.Empty;
+                return RcImmutableArray<DtMeshTile>.Empty;
             }
 
             RcVec3f bmin = center.Subtract(halfExtents);
diff --git a/src/DotRecast.Recast.Demo/Draw/DrawMode.cs b/src/DotRecast.Recast.Demo/Draw/DrawMode.cs
index c75a0a2..8e5aba5 100644
--- a/src/DotRecast.Recast.Demo/Draw/DrawMode.cs
+++ b/src/DotRecast.Recast.Demo/Draw/DrawMode.cs
@@ -19,6 +19,7 @@ freely, subject to the following restrictions:
 */
 
 using System.Collections.Immutable;
+using DotRecast.Core;
 
 namespace DotRecast.Recast.Demo.Draw;
 
@@ -43,7 +44,7 @@ public class DrawMode
     public static readonly DrawMode DRAWMODE_POLYMESH = new(16, "Poly Mesh");
     public static readonly DrawMode DRAWMODE_POLYMESH_DETAIL = new(17, "Poly Mesh Detils");
 
-    public static readonly ImmutableArray<DrawMode> Values = ImmutableArray.Create(
+    public static readonly RcImmutableArray<DrawMode> Values = RcImmutableArray.Create(
         DRAWMODE_MESH,
         DRAWMODE_NAVMESH,
         DRAWMODE_NAVMESH_INVIS,
diff --git a/src/DotRecast.Recast.Toolset/Builder/SampleAreaModifications.cs b/src/DotRecast.Recast.Toolset/Builder/SampleAreaModifications.cs
index 6fa28d6..b754ee1 100644
--- a/src/DotRecast.Recast.Toolset/Builder/SampleAreaModifications.cs
+++ b/src/DotRecast.Recast.Toolset/Builder/SampleAreaModifications.cs
@@ -18,8 +18,8 @@ freely, subject to the following restrictions:
 3. This notice may not be removed or altered from any source distribution.
 */
 
-using System.Collections.Immutable;
 using System.Linq;
+using DotRecast.Core;
 
 namespace DotRecast.Recast.Toolset.Builder
 {
@@ -49,7 +49,7 @@ namespace DotRecast.Recast.Toolset.Builder
         public static readonly RcAreaModification SAMPLE_AREAMOD_DOOR = new RcAreaModification(SAMPLE_POLYAREA_TYPE_DOOR);
         public static readonly RcAreaModification SAMPLE_AREAMOD_JUMP = new RcAreaModification(SAMPLE_POLYAREA_TYPE_JUMP);
 
-        public static readonly ImmutableArray<RcAreaModification> Values = ImmutableArray.Create(
+        public static readonly RcImmutableArray<RcAreaModification> Values = RcImmutableArray.Create(
             SAMPLE_AREAMOD_WALKABLE,
             SAMPLE_AREAMOD_GROUND,
             SAMPLE_AREAMOD_WATER,
diff --git a/src/DotRecast.Recast.Toolset/Builder/SoloNavMeshBuilder.cs b/src/DotRecast.Recast.Toolset/Builder/SoloNavMeshBuilder.cs
index 497491d..3295f3f 100644
--- a/src/DotRecast.Recast.Toolset/Builder/SoloNavMeshBuilder.cs
+++ b/src/DotRecast.Recast.Toolset/Builder/SoloNavMeshBuilder.cs
@@ -18,7 +18,7 @@ freely, subject to the following restrictions:
 
 using System;
 using System.Collections.Generic;
-using System.Collections.Immutable;
+using DotRecast.Core;
 using DotRecast.Detour;
 using DotRecast.Recast.Toolset.Geom;
 
@@ -55,7 +55,7 @@ namespace DotRecast.Recast.Toolset.Builder
             }
 
             var navMesh = BuildNavMesh(meshData, vertsPerPoly);
-            return new NavMeshBuildResult(ImmutableArray.Create(rcResult), navMesh);
+            return new NavMeshBuildResult(RcImmutableArray.Create(rcResult), navMesh);
         }
 
         private DtNavMesh BuildNavMesh(DtMeshData meshData, int vertsPerPoly)
diff --git a/src/DotRecast.Recast.Toolset/Geom/DemoInputGeomProvider.cs b/src/DotRecast.Recast.Toolset/Geom/DemoInputGeomProvider.cs
index f6f440d..a25aae8 100644
--- a/src/DotRecast.Recast.Toolset/Geom/DemoInputGeomProvider.cs
+++ b/src/DotRecast.Recast.Toolset/Geom/DemoInputGeomProvider.cs
@@ -20,7 +20,6 @@ freely, subject to the following restrictions:
 
 using System;
 using System.Collections.Generic;
-using System.Collections.Immutable;
 using DotRecast.Core;
 using DotRecast.Recast.Geom;
 
@@ -107,7 +106,7 @@ namespace DotRecast.Recast.Toolset.Geom
 
         public IEnumerable<RcTriMesh> Meshes()
         {
-            return ImmutableArray.Create(_mesh);
+            return RcImmutableArray.Create(_mesh);
         }
 
         public List<DemoOffMeshConnection> GetOffMeshConnections()
diff --git a/src/DotRecast.Recast.Toolset/Tools/CrowdToolMode.cs b/src/DotRecast.Recast.Toolset/Tools/CrowdToolMode.cs
index ac5549a..f5bd0b8 100644
--- a/src/DotRecast.Recast.Toolset/Tools/CrowdToolMode.cs
+++ b/src/DotRecast.Recast.Toolset/Tools/CrowdToolMode.cs
@@ -1,4 +1,4 @@
-using System.Collections.Immutable;
+using DotRecast.Core;
 
 namespace DotRecast.Recast.Toolset.Tools
 {
@@ -10,7 +10,7 @@ namespace DotRecast.Recast.Toolset.Tools
         public static readonly CrowdToolMode TOGGLE_POLYS = new CrowdToolMode(3, "Toggle Polys");
         public static readonly CrowdToolMode PROFILING = new CrowdToolMode(4, "Profiling");
 
-        public static readonly ImmutableArray<CrowdToolMode> Values = ImmutableArray.Create(
+        public static readonly RcImmutableArray<CrowdToolMode> Values = RcImmutableArray.Create(
             CREATE,
             MOVE_TARGET,
             SELECT,
diff --git a/src/DotRecast.Recast.Toolset/Tools/DynamicUpdateToolMode.cs b/src/DotRecast.Recast.Toolset/Tools/DynamicUpdateToolMode.cs
index 2bccd99..95b0a92 100644
--- a/src/DotRecast.Recast.Toolset/Tools/DynamicUpdateToolMode.cs
+++ b/src/DotRecast.Recast.Toolset/Tools/DynamicUpdateToolMode.cs
@@ -1,4 +1,4 @@
-using System.Collections.Immutable;
+using DotRecast.Core;
 
 namespace DotRecast.Recast.Toolset.Tools
 {
@@ -8,7 +8,7 @@ namespace DotRecast.Recast.Toolset.Tools
         public static readonly DynamicUpdateToolMode COLLIDERS = new DynamicUpdateToolMode(1, "Colliders");
         public static readonly DynamicUpdateToolMode RAYCAST = new DynamicUpdateToolMode(2, "Raycast");
 
-        public static readonly ImmutableArray<DynamicUpdateToolMode> Values = ImmutableArray.Create(
+        public static readonly RcImmutableArray<DynamicUpdateToolMode> Values = RcImmutableArray.Create(
             BUILD, COLLIDERS, RAYCAST
         );
 
diff --git a/src/DotRecast.Recast.Toolset/Tools/TestNavmeshToolMode.cs b/src/DotRecast.Recast.Toolset/Tools/TestNavmeshToolMode.cs
index cfe7dd8..57cc8eb 100644
--- a/src/DotRecast.Recast.Toolset/Tools/TestNavmeshToolMode.cs
+++ b/src/DotRecast.Recast.Toolset/Tools/TestNavmeshToolMode.cs
@@ -1,4 +1,4 @@
-using System.Collections.Immutable;
+using DotRecast.Core;
 
 namespace DotRecast.Recast.Toolset.Tools
 {
@@ -14,7 +14,7 @@ namespace DotRecast.Recast.Toolset.Tools
         public static readonly TestNavmeshToolMode FIND_LOCAL_NEIGHBOURHOOD = new TestNavmeshToolMode(7, "Find Local Neighbourhood");
         public static readonly TestNavmeshToolMode RANDOM_POINTS_IN_CIRCLE = new TestNavmeshToolMode(8, "Random Points in Circle");
 
-        public static readonly ImmutableArray<TestNavmeshToolMode> Values = ImmutableArray.Create(
+        public static readonly RcImmutableArray<TestNavmeshToolMode> Values = RcImmutableArray.Create(
             PATHFIND_FOLLOW,
             PATHFIND_STRAIGHT,
             PATHFIND_SLICED,
diff --git a/src/DotRecast.Recast.Toolset/Tools/TileToolImpl.cs b/src/DotRecast.Recast.Toolset/Tools/TileToolImpl.cs
index eb6e165..d28d613 100644
--- a/src/DotRecast.Recast.Toolset/Tools/TileToolImpl.cs
+++ b/src/DotRecast.Recast.Toolset/Tools/TileToolImpl.cs
@@ -1,5 +1,4 @@
 using System.Linq;
-using System.Collections.Immutable;
 using DotRecast.Core;
 using DotRecast.Recast.Toolset.Builder;
 
@@ -130,8 +129,7 @@ namespace DotRecast.Recast.Toolset.Tools
 
             var tb = new TileNavMeshBuilder();
             var meshData = tb.BuildMeshData(geom,
-                settings.cellSize, settings.cellHeight, settings.agentHeight, settings.agentRadius, settings.agentMaxClimb,
-                ImmutableArray.Create(result)
+                settings.cellSize, settings.cellHeight, settings.agentHeight, settings.agentRadius, settings.agentMaxClimb, RcImmutableArray.Create(result)
             ).FirstOrDefault();
 
             if (null == meshData)
diff --git a/src/DotRecast.Recast/Geom/SimpleInputGeomProvider.cs b/src/DotRecast.Recast/Geom/SimpleInputGeomProvider.cs
index c2f06c2..0590827 100644
--- a/src/DotRecast.Recast/Geom/SimpleInputGeomProvider.cs
+++ b/src/DotRecast.Recast/Geom/SimpleInputGeomProvider.cs
@@ -20,7 +20,6 @@ freely, subject to the following restrictions:
 
 using System;
 using System.Collections.Generic;
-using System.Collections.Immutable;
 using DotRecast.Core;
 
 namespace DotRecast.Recast.Geom
@@ -108,7 +107,7 @@ namespace DotRecast.Recast.Geom
 
         public IEnumerable<RcTriMesh> Meshes()
         {
-            return ImmutableArray.Create(_mesh);
+            return RcImmutableArray.Create(_mesh);
         }
 
         public void CalculateNormals()
diff --git a/src/DotRecast.Recast/Geom/SingleTrimeshInputGeomProvider.cs b/src/DotRecast.Recast/Geom/SingleTrimeshInputGeomProvider.cs
index b703aba..f5e3284 100644
--- a/src/DotRecast.Recast/Geom/SingleTrimeshInputGeomProvider.cs
+++ b/src/DotRecast.Recast/Geom/SingleTrimeshInputGeomProvider.cs
@@ -18,7 +18,6 @@ freely, subject to the following restrictions:
 
 using System;
 using System.Collections.Generic;
-using System.Collections.Immutable;
 using DotRecast.Core;
 
 namespace DotRecast.Recast.Geom
@@ -56,12 +55,12 @@ namespace DotRecast.Recast.Geom
 
         public IEnumerable<RcTriMesh> Meshes()
         {
-            return ImmutableArray.Create(_mesh);
+            return RcImmutableArray.Create(_mesh);
         }
 
         public IList<RcConvexVolume> ConvexVolumes()
         {
-            return ImmutableArray<RcConvexVolume>.Empty;
+            return RcImmutableArray<RcConvexVolume>.Empty;
         }
     }
 }
\ No newline at end of file