diff --git a/src/main/java/net/minecraftforge/common/BiomeManager.java b/src/main/java/net/minecraftforge/common/BiomeManager.java
index cde6250f3d..c803d64454 100644
--- a/src/main/java/net/minecraftforge/common/BiomeManager.java
+++ b/src/main/java/net/minecraftforge/common/BiomeManager.java
@@ -22,6 +22,7 @@ package net.minecraftforge.common;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 
 import com.google.common.collect.ImmutableList;
@@ -35,6 +36,7 @@ public class BiomeManager
 {
     private static TrackedList<BiomeEntry>[] biomes = setupBiomes();
     private static final List<RegistryKey<Biome>> additionalOverworldBiomes = new ArrayList<>();
+    private static final List<RegistryKey<Biome>> additionalOverworldBiomesView = Collections.unmodifiableList(additionalOverworldBiomes);
 
     private static TrackedList<BiomeEntry>[] setupBiomes()
     {
@@ -101,8 +103,9 @@ public class BiomeManager
     /**
      * Add biomes that you add to the overworld without using {@link BiomeManager#addBiome(BiomeType, BiomeEntry)}
      */
-    public static void addAdditionalOverworldBiomes(RegistryKey<Biome> biome){
-        if (!"minecraft".equals(biome.func_240901_a_().getNamespace()) && additionalOverworldBiomes.stream().noneMatch(entry -> entry.func_240901_a_().equals(biome.func_240901_a_())))
+    public static void addAdditionalOverworldBiomes(RegistryKey<Biome> biome)
+    {
+        if (!"minecraft".equals(biome.getLocation().getNamespace()) && additionalOverworldBiomes.stream().noneMatch(entry -> entry.getLocation().equals(biome.getLocation())))
         {
             additionalOverworldBiomes.add(biome);
         }
@@ -112,7 +115,7 @@ public class BiomeManager
     {
         int idx = type.ordinal();
         List<BiomeEntry> list = idx > biomes.length ? null : biomes[idx];
-        if(list != null)
+        if (list != null)
         {
             additionalOverworldBiomes.add(entry.key);
             return list.add(entry);
@@ -132,7 +135,7 @@ public class BiomeManager
      */
     public static List<RegistryKey<Biome>> getAdditionalOverworldBiomes()
     {
-        return additionalOverworldBiomes;
+        return additionalOverworldBiomesView;
     }
 
     public static ImmutableList<BiomeEntry> getBiomes(BiomeType type)