diff --git a/src/main/java/carpet/mixins/UpdateStructureBlockC2SPacketMixin.java b/src/main/java/carpet/mixins/UpdateStructureBlockC2SPacketMixin.java
index 4be905f1..e67f342a 100644
--- a/src/main/java/carpet/mixins/UpdateStructureBlockC2SPacketMixin.java
+++ b/src/main/java/carpet/mixins/UpdateStructureBlockC2SPacketMixin.java
@@ -8,7 +8,9 @@ import net.minecraft.network.packet.c2s.play.UpdateStructureBlockC2SPacket;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.MathHelper;
 import net.minecraft.util.math.Vec3i;
+import org.spongepowered.asm.mixin.Final;
 import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Mutable;
 import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Inject;
@@ -16,9 +18,9 @@ import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
 @Mixin(UpdateStructureBlockC2SPacket.class)
 public class UpdateStructureBlockC2SPacketMixin {
-    @Shadow
+    @Mutable @Final @Shadow
     private BlockPos offset;
-    @Shadow
+    @Mutable @Final @Shadow
     private Vec3i size;
 
     @Inject(