diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index bb244f9f5..0dd4bb822 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -954,6 +954,7 @@ public class CraftWorld implements World {
 
     @Override
     public void setBiome(int x, int y, int z, Biome bio) {
+        Preconditions.checkArgument(bio != Biome.CUSTOM, "Cannot set the biome to %s", bio);
         BiomeBase bb = CraftBlock.biomeToBiomeBase(getHandle().r().b(IRegistry.ay), bio);
         BlockPosition pos = new BlockPosition(x, 0, z);
         if (this.world.isLoaded(pos)) {
diff --git a/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java b/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
index 7654c0f8b..d7bcdd80d 100644
--- a/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
+++ b/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
@@ -499,11 +499,12 @@ public class CraftBlock implements Block {
             return null;
         }
 
-        return Registry.BIOME.get(CraftNamespacedKey.fromMinecraft(registry.getKey(base)));
+        Biome biome = Registry.BIOME.get(CraftNamespacedKey.fromMinecraft(registry.getKey(base)));
+        return (biome == null) ? Biome.CUSTOM : biome;
     }
 
     public static BiomeBase biomeToBiomeBase(IRegistry<BiomeBase> registry, Biome bio) {
-        if (bio == null) {
+        if (bio == null || bio == Biome.CUSTOM) {
             return null;
         }
 
diff --git a/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java b/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java
index 3e6d78a1f..7ce7e1303 100644
--- a/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java
+++ b/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java
@@ -65,6 +65,7 @@ public class CustomChunkGenerator extends InternalChunkGenerator {
 
         @Override
         public void setBiome(int x, int y, int z, Biome bio) {
+            Preconditions.checkArgument(bio != Biome.CUSTOM, "Cannot set the biome to %s", bio);
             biome.setBiome(x >> 2, y >> 2, z >> 2, CraftBlock.biomeToBiomeBase((IRegistry<BiomeBase>) biome.registry, bio));
         }
     }
diff --git a/src/test/java/org/bukkit/BiomeTest.java b/src/test/java/org/bukkit/BiomeTest.java
index 7105dbfe6..3f478abc0 100644
--- a/src/test/java/org/bukkit/BiomeTest.java
+++ b/src/test/java/org/bukkit/BiomeTest.java
@@ -13,14 +13,19 @@ public class BiomeTest extends AbstractTestingBase {
     @Test
     public void testBukkitToMinecraft() {
         for (Biome biome : Biome.values()) {
+            if (biome == Biome.CUSTOM) {
+                continue;
+            }
+
             Assert.assertNotNull("No NMS mapping for " + biome, CraftBlock.biomeToBiomeBase(RegistryGeneration.WORLDGEN_BIOME, biome));
         }
     }
 
     @Test
     public void testMinecraftToBukkit() {
-        for (Object biome : RegistryGeneration.WORLDGEN_BIOME) {
-            Assert.assertNotNull("No Bukkit mapping for " + biome, CraftBlock.biomeBaseToBiome(RegistryGeneration.WORLDGEN_BIOME, (BiomeBase) biome));
+        for (BiomeBase biomeBase : RegistryGeneration.WORLDGEN_BIOME) {
+            Biome biome = CraftBlock.biomeBaseToBiome(RegistryGeneration.WORLDGEN_BIOME, biomeBase);
+            Assert.assertTrue("No Bukkit mapping for " + biomeBase, biome != null && biome != Biome.CUSTOM);
         }
     }
 }