--- a/net/minecraft/world/effect/PoisonMobEffect.java
+++ b/net/minecraft/world/effect/PoisonMobEffect.java
@@ -13,7 +_,7 @@
     @Override
     public boolean applyEffectTick(ServerLevel level, LivingEntity entity, int amplifier) {
         if (entity.getHealth() > 1.0F) {
-            entity.hurtServer(level, entity.damageSources().magic(), 1.0F);
+            entity.hurtServer(level, entity.damageSources().magic().knownCause(org.bukkit.event.entity.EntityDamageEvent.DamageCause.POISON), 1.0F); // CraftBukkit
         }
 
         return true;
