diff --git a/src/main/kotlin/ru/dbotthepony/mc/otm/worldgen/placement/EnormousPlacement.kt b/src/main/kotlin/ru/dbotthepony/mc/otm/worldgen/placement/EnormousPlacement.kt
index ea6f2933b..b2580eef4 100644
--- a/src/main/kotlin/ru/dbotthepony/mc/otm/worldgen/placement/EnormousPlacement.kt
+++ b/src/main/kotlin/ru/dbotthepony/mc/otm/worldgen/placement/EnormousPlacement.kt
@@ -7,6 +7,7 @@ import com.mojang.serialization.Codec
 import com.mojang.serialization.MapCodec
 import com.mojang.serialization.codecs.RecordCodecBuilder
 import it.unimi.dsi.fastutil.io.FastByteArrayOutputStream
+import it.unimi.dsi.fastutil.objects.ObjectOpenHashSet
 import net.minecraft.Util
 import net.minecraft.core.BlockPos
 import net.minecraft.core.SectionPos
@@ -50,7 +51,7 @@ class EnormousPlacement(
 ) : PlacementModifier() {
 	private class GeneratedChunk(positions: Stream<BlockPos>) {
 		// TODO: memory inefficient
-		private val positions = ArrayList<BlockPos>()
+		private val positions = ObjectOpenHashSet<BlockPos>()
 
 		init {
 			positions.forEach { this.positions.add(it) }