diff --git a/Common/src/main/java/terrablender/mixin/MixinParameterList.java b/Common/src/main/java/terrablender/mixin/MixinParameterList.java
index 4d941f3..ca0a06b 100644
--- a/Common/src/main/java/terrablender/mixin/MixinParameterList.java
+++ b/Common/src/main/java/terrablender/mixin/MixinParameterList.java
@@ -76,7 +76,10 @@ public void initializeForTerraBlender(RegistryAccess registryAccess, RegionType
             else
             {
                 ImmutableList.Builder<Pair<Climate.ParameterPoint, Holder<Biome>>> builder = ImmutableList.builder();
-                region.addBiomes(biomeRegistry, pair -> builder.add(pair.mapSecond(biomeRegistry::getHolderOrThrow)));
+                region.addBiomes(biomeRegistry, pair -> {
+                    if (biomeRegistry.getHolder(pair.getSecond()).isPresent())
+                        builder.add(pair.mapSecond(biomeRegistry::getHolderOrThrow));
+                });
                 ImmutableList<Pair<Climate.ParameterPoint, Holder<Biome>>> uniqueValues = builder.build();
 
                 // We can't create an RTree if there are no values present.
diff --git a/Common/src/main/java/terrablender/util/LevelUtils.java b/Common/src/main/java/terrablender/util/LevelUtils.java
index 0c9e5f9..1d4dc74 100644
--- a/Common/src/main/java/terrablender/util/LevelUtils.java
+++ b/Common/src/main/java/terrablender/util/LevelUtils.java
@@ -102,7 +102,10 @@ public static void initializeBiomes(RegistryAccess registryAccess, Holder<Dimens
         // Append modded biomes to the biome source biome list
         Registry<Biome> biomeRegistry = registryAccess.registryOrThrow(Registries.BIOME);
         ImmutableList.Builder<Holder<Biome>> builder = ImmutableList.builder();
-        Regions.get(regionType).forEach(region -> region.addBiomes(biomeRegistry, pair -> builder.add(biomeRegistry.getHolderOrThrow(pair.getSecond()))));
+        Regions.get(regionType).forEach(region -> region.addBiomes(biomeRegistry, pair -> {
+            if (biomeRegistry.getHolder(pair.getSecond()).isPresent())
+                builder.add(biomeRegistry.getHolderOrThrow(pair.getSecond()));
+        }));
         biomeSourceEx.appendDeferredBiomesList(builder.build());
 
         TerraBlender.LOGGER.info(String.format("Initialized TerraBlender biomes for level stem %s", levelResourceKey.location()));