diff --git a/src/main/java/de/bixilon/minosoft/data/registries/blocks/light/DirectedProperty.kt b/src/main/java/de/bixilon/minosoft/data/registries/blocks/light/DirectedProperty.kt
index 92f513e3d..60193d4a5 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/blocks/light/DirectedProperty.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/blocks/light/DirectedProperty.kt
@@ -18,6 +18,7 @@ import de.bixilon.minosoft.data.direction.Directions
 import de.bixilon.minosoft.data.registries.shapes.VoxelShape
 import de.bixilon.minosoft.data.registries.shapes.side.VoxelSide
 import de.bixilon.minosoft.data.registries.shapes.side.VoxelSideSet
+import it.unimi.dsi.fastutil.objects.ObjectOpenHashSet
 
 class DirectedProperty(
     private val directions: BooleanArray,
@@ -72,7 +73,7 @@ class DirectedProperty(
             // ToDo: This whole calculation is technically wrong, it could be that 2 different sides of 2 blocks are "free". That means that light can still not pass the blocks, but
             // this algorithm does not cover it. Let's see it as performance hack
 
-            val sides: MutableSet<VoxelSide> = mutableSetOf()
+            val sides: MutableSet<VoxelSide> = ObjectOpenHashSet()
 
             for (aabb in this) {
                 when (side.axis) {
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/shapes/side/VoxelSideSet.kt b/src/main/java/de/bixilon/minosoft/data/registries/shapes/side/VoxelSideSet.kt
index d74cb8de1..9910d6833 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/shapes/side/VoxelSideSet.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/shapes/side/VoxelSideSet.kt
@@ -13,6 +13,8 @@
 
 package de.bixilon.minosoft.data.registries.shapes.side
 
+import it.unimi.dsi.fastutil.objects.ObjectOpenHashSet
+
 class VoxelSideSet(
     val sides: Set<VoxelSide>,
 ) : Iterable<VoxelSide> {
@@ -28,7 +30,7 @@ class VoxelSideSet(
             return this
         }
 
-        val next: MutableSet<VoxelSide> = mutableSetOf()
+        val next: MutableSet<VoxelSide> = ObjectOpenHashSet()
 
         val array = this.sides.toTypedArray()
         for (i in 1 until sides.size) {