diff --git a/src/main/java/net/minestom/server/instance/DynamicChunk.java b/src/main/java/net/minestom/server/instance/DynamicChunk.java
index 218554b80..66044667f 100644
--- a/src/main/java/net/minestom/server/instance/DynamicChunk.java
+++ b/src/main/java/net/minestom/server/instance/DynamicChunk.java
@@ -19,6 +19,8 @@ import java.util.concurrent.CopyOnWriteArraySet;
 public class DynamicChunk extends Chunk {
 
     // blocks id based on coordinate, see Chunk#getBlockIndex
+    // WARNING: those arrays are NOT thread-safe
+    // and modifying them can cause issue with block data, update, block entity and the cached chunk packet
     protected final short[] blocksStateId = new short[CHUNK_SIZE_X * CHUNK_SIZE_Y * CHUNK_SIZE_Z];
     protected final short[] customBlocksId = new short[CHUNK_SIZE_X * CHUNK_SIZE_Y * CHUNK_SIZE_Z];