diff --git a/dependencies.gradle b/dependencies.gradle
index fb48f55..37d47bb 100644
--- a/dependencies.gradle
+++ b/dependencies.gradle
@@ -1,4 +1,5 @@
 
 dependencies {
     api('com.github.GTNewHorizons:NotEnoughIds:2.1.6:dev')
+    api("com.github.GTNewHorizons:GTNHLib:0.6.21:dev")
 }
diff --git a/src/main/java/com/gtnewhorizons/postea/api/BlockReplacementManager.java b/src/main/java/com/gtnewhorizons/postea/api/BlockReplacementManager.java
index c6bfaaf..44259dd 100644
--- a/src/main/java/com/gtnewhorizons/postea/api/BlockReplacementManager.java
+++ b/src/main/java/com/gtnewhorizons/postea/api/BlockReplacementManager.java
@@ -1,7 +1,6 @@
 package com.gtnewhorizons.postea.api;
 
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Map;
 import java.util.function.BiFunction;
 
@@ -9,10 +8,12 @@ import net.minecraft.world.World;
 
 import com.gtnewhorizons.postea.utility.BlockConversionInfo;
 
+import it.unimi.dsi.fastutil.ints.IntOpenHashSet;
+
 public class BlockReplacementManager {
 
     public static final Map<String, BiFunction<BlockConversionInfo, World, BlockConversionInfo>> blockReplacementMap = new HashMap<>();
-    public static final HashSet<Integer> posteaMarkedIDs = new HashSet<>();
+    public static final IntOpenHashSet posteaMarkedIDs = new IntOpenHashSet();
 
     @SuppressWarnings("unused")
     public static void addBlockReplacement(String blockNameIn,