diff --git a/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BiomeConfig.java b/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BiomeConfig.java
index d6d296d4..51ce91fb 100644
--- a/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BiomeConfig.java
+++ b/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BiomeConfig.java
@@ -25,8 +25,9 @@
 package de.bluecolored.bluemap.core.config;
 
 import java.io.IOException;
-import java.util.HashMap;
+import java.util.Map;
 import java.util.Map.Entry;
+import java.util.concurrent.ConcurrentHashMap;
 
 import de.bluecolored.bluemap.core.logger.Logger;
 import de.bluecolored.bluemap.core.mca.mapping.BiomeMapper;
@@ -37,7 +38,7 @@
 public class BiomeConfig implements BiomeMapper {
 
 	private ConfigurationLoader<? extends ConfigurationNode> autopoulationConfigLoader;
-	private HashMap<Integer, Biome> biomes;
+	private Map<Integer, Biome> biomes;
 	
 	public BiomeConfig(ConfigurationNode node) {
 		this(node, null);
@@ -46,7 +47,7 @@ public BiomeConfig(ConfigurationNode node) {
 	public BiomeConfig(ConfigurationNode node, ConfigurationLoader<? extends ConfigurationNode> autopoulationConfigLoader) {
 		this.autopoulationConfigLoader = autopoulationConfigLoader;
 		
-		biomes = new HashMap<>();
+		biomes = new ConcurrentHashMap<>(200, 0.5f, 8);
 
 		for (Entry<Object, ? extends ConfigurationNode> e : node.getChildrenMap().entrySet()){
 			String id = e.getKey().toString();
diff --git a/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockIdConfig.java b/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockIdConfig.java
index 1ee5360a..a3b7426e 100644
--- a/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockIdConfig.java
+++ b/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockIdConfig.java
@@ -25,9 +25,11 @@
 package de.bluecolored.bluemap.core.config;
 
 import java.io.IOException;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.concurrent.ConcurrentHashMap;
+
+import com.google.common.base.Preconditions;
 
 import de.bluecolored.bluemap.core.logger.Logger;
 import de.bluecolored.bluemap.core.mca.mapping.BlockIdMapper;
@@ -48,8 +50,8 @@ public BlockIdConfig(ConfigurationNode node) {
 	public BlockIdConfig(ConfigurationNode node, ConfigurationLoader<? extends ConfigurationNode> autopoulationConfigLoader) {
 		this.autopoulationConfigLoader = autopoulationConfigLoader;
 		
-		numeralMappings = new HashMap<>(); 
-		idMappings = new HashMap<>(); 
+		numeralMappings = new ConcurrentHashMap<>(200, 0.5f, 8); 
+		idMappings = new ConcurrentHashMap<>(200, 0.5f, 8); 
 		
 		for (Entry<Object, ? extends ConfigurationNode> e : node.getChildrenMap().entrySet()){
 			String key = e.getKey().toString();
@@ -135,7 +137,7 @@ public BlockState get(String id, int numeralId, int meta) {
 				}
 				
 				idMappings.put(idmeta, state);
-				numeralMappings.put(numidmeta, state);
+				Preconditions.checkArgument(numeralMappings.put(numidmeta, state) == null);
 				
 				if (autopoulationConfigLoader != null) {
 					synchronized (autopoulationConfigLoader) {
diff --git a/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockPropertiesConfig.java b/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockPropertiesConfig.java
index 8b9f771b..9949cf1e 100644
--- a/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockPropertiesConfig.java
+++ b/BlueMapCore/src/main/java/de/bluecolored/bluemap/core/config/BlockPropertiesConfig.java
@@ -33,6 +33,7 @@
 import com.google.common.cache.LoadingCache;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.MultimapBuilder;
+import com.google.common.collect.Multimaps;
 
 import de.bluecolored.bluemap.core.logger.Logger;
 import de.bluecolored.bluemap.core.mca.mapping.BlockPropertiesMapper;
@@ -61,7 +62,7 @@ public BlockPropertiesConfig(ConfigurationNode node, ResourcePack resourcePack,
 		this.resourcePack = resourcePack;
 		this.autopoulationConfigLoader = autopoulationConfigLoader;
 		
-		mappings = MultimapBuilder.hashKeys().arrayListValues().build();
+		mappings = Multimaps.synchronizedListMultimap(MultimapBuilder.hashKeys().arrayListValues().build());
 		
 		for (Entry<Object, ? extends ConfigurationNode> e : node.getChildrenMap().entrySet()){
 			String key = e.getKey().toString();