diff --git a/src/AcDream.Core/Physics/CellTransit.cs b/src/AcDream.Core/Physics/CellTransit.cs
index 4a6f964..ae19e70 100644
--- a/src/AcDream.Core/Physics/CellTransit.cs
+++ b/src/AcDream.Core/Physics/CellTransit.cs
@@ -49,7 +49,7 @@ public static class CellTransit
         uint currentCellId,
         Vector3 worldSphereCenter,
         float sphereRadius,
-        HashSet<uint> candidates,
+        ICollection<uint> candidates,
         out bool exitOutside)
     {
         var spheres = new[]
@@ -77,7 +77,7 @@ public static class CellTransit
         uint currentCellId,
         IReadOnlyList<Sphere> worldSpheres,
         int numSpheres,
-        HashSet<uint> candidates,
+        ICollection<uint> candidates,
         out bool exitOutside)
     {
         exitOutside = false;
@@ -213,7 +213,7 @@ public static class CellTransit
         Vector3 worldSphereCenter,
         float sphereRadius,
         uint currentCellId,
-        HashSet<uint> candidates)
+        ICollection<uint> candidates)
     {
         const float CellSize = 24f;
 
@@ -257,7 +257,7 @@ public static class CellTransit
         IReadOnlyList<Sphere> worldSpheres,
         int numSpheres,
         uint currentCellId,
-        HashSet<uint> candidates)
+        ICollection<uint> candidates)
     {
         int sphereCount = EffectiveSphereCount(worldSpheres, numSpheres);
         for (int i = 0; i < sphereCount; i++)
@@ -267,7 +267,7 @@ public static class CellTransit
         }
     }
 
-    private static void AddOutsideCell(HashSet<uint> candidates, uint lbPrefix, int gridX, int gridY)
+    private static void AddOutsideCell(ICollection<uint> candidates, uint lbPrefix, int gridX, int gridY)
     {
         if (gridX < 0 || gridX >= 8 || gridY < 0 || gridY >= 8) return;
 
@@ -301,7 +301,7 @@ public static class CellTransit
         BuildingPhysics building,
         Vector3 worldSphereCenter,
         float sphereRadius,
-        HashSet<uint> candidates)
+        ICollection<uint> candidates)
     {
         foreach (var portal in building.Portals)
         {