diff --git a/src/server/scripts/Northrend/Naxxramas/boss_thaddius.cpp b/src/server/scripts/Northrend/Naxxramas/boss_thaddius.cpp
index efe7c6956..200a3962c 100644
--- a/src/server/scripts/Northrend/Naxxramas/boss_thaddius.cpp
+++ b/src/server/scripts/Northrend/Naxxramas/boss_thaddius.cpp
@@ -683,22 +683,18 @@ public:
     };
 };
 
-class at_thaddius_entrance : public AreaTriggerScript
+class at_thaddius_entrance : public OnlyOnceAreaTriggerScript
 {
 public:
-    at_thaddius_entrance() : AreaTriggerScript("at_thaddius_entrance") { }
+    at_thaddius_entrance() : OnlyOnceAreaTriggerScript("at_thaddius_entrance") { }
 
-    bool OnTrigger(Player* player, AreaTrigger const* /*areaTrigger*/) override
+    bool _OnTrigger(Player* player, const AreaTrigger* /*trigger*/) override
     {
-        InstanceScript* instance = player->GetInstanceScript();
-        if (!instance || instance->GetData(DATA_THADDIUS_INTRO) || instance->GetBossState(BOSS_THADDIUS) == DONE)
-            return true;
-
-        if (Creature* thaddius = instance->GetCreature(DATA_THADDIUS_BOSS))
-            thaddius->AI()->Talk(SAY_GREET);
-
-        instance->SetData(DATA_THADDIUS_INTRO, 1);
-        return true;
+        if (InstanceScript* instance = player->GetInstanceScript())
+            if (instance->GetBossState(BOSS_THADDIUS) != DONE)
+                if (Creature* thaddius = instance->GetCreature(DATA_THADDIUS_BOSS))
+                    thaddius->AI()->Talk(SAY_GREET);
+        return false;
     }
 };
 
diff --git a/src/server/scripts/Northrend/Naxxramas/naxxramas.h b/src/server/scripts/Northrend/Naxxramas/naxxramas.h
index 6f47c4fa1..4b790f1cc 100644
--- a/src/server/scripts/Northrend/Naxxramas/naxxramas.h
+++ b/src/server/scripts/Northrend/Naxxramas/naxxramas.h
@@ -75,17 +75,15 @@ enum NaxxramasData
     DATA_DANCE_FAIL                 = 301,
     DATA_SPORE_KILLED               = 302,
     DATA_FRENZY_REMOVED             = 303,
-    DATA_THADDIUS_INTRO             = 304,
-    DATA_CHARGES_CROSSED            = 305,
-    DATA_HUNDRED_CLUB               = 306,
-    DATA_ABOMINATION_KILLED         = 307,
+    DATA_CHARGES_CROSSED            = 304,
+    DATA_HUNDRED_CLUB               = 305,
+    DATA_ABOMINATION_KILLED         = 306,
 };
 
 enum NaxxramasPersistentData
 {
-    PERSISTENT_DATA_THADDIUS_INTRO   = 0,
-    PERSISTENT_DATA_KELTHUZAD_DIALOG = 1,
-    PERSISTENT_DATA_IMMORTAL_FAIL    = 2,
+    PERSISTENT_DATA_KELTHUZAD_DIALOG = 0,
+    PERSISTENT_DATA_IMMORTAL_FAIL    = 1,
     PERSISTENT_DATA_COUNT
 };