diff --git a/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java b/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java
index 715e686a..6c5b866d 100644
--- a/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java
+++ b/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java
@@ -339,6 +339,10 @@ public final class BlockItemPackets1_17 extends BackwardsItemRewriter<Clientboun
 
             CompoundTag heightMaps = chunk.getHeightMap();
             for (Tag heightMapTag : heightMaps.values()) {
+                if (!(heightMapTag instanceof LongArrayTag)) {
+                    continue; // Client can handle bad data
+                }
+
                 LongArrayTag heightMap = (LongArrayTag) heightMapTag;
                 int[] heightMapData = new int[256];
                 int bitsPerEntry = MathUtil.ceilLog2((currentWorldSectionHeight << 4) + 1);