diff --git a/src/server/scripts/Northrend/Naxxramas/instance_naxxramas.cpp b/src/server/scripts/Northrend/Naxxramas/instance_naxxramas.cpp
index 918853184..a6498b867 100644
--- a/src/server/scripts/Northrend/Naxxramas/instance_naxxramas.cpp
+++ b/src/server/scripts/Northrend/Naxxramas/instance_naxxramas.cpp
@@ -426,20 +426,49 @@ public:
             case ACHIEV_CRITERIA_THE_HUNDRED_CLUB_25_PLAYER:
                 return _sapphironAchievement;
             case ACHIEV_CRITERIA_THE_UNDYING_KELTHUZAD:
-            case ACHIEV_CRITERIA_THE_UNDYING_THE_FOUR_HORSEMEN:
-            case ACHIEV_CRITERIA_THE_UNDYING_MAEXXNA:
-            case ACHIEV_CRITERIA_THE_UNDYING_LOATHEB:
-            case ACHIEV_CRITERIA_THE_UNDYING_THADDIUS:
             case ACHIEV_CRITERIA_THE_IMMORTAL_KELTHUZAD:
+            case ACHIEV_CRITERIA_THE_UNDYING_THE_FOUR_HORSEMEN:
             case ACHIEV_CRITERIA_THE_IMMORTAL_THE_FOUR_HORSEMEN:
+            case ACHIEV_CRITERIA_THE_UNDYING_MAEXXNA:
             case ACHIEV_CRITERIA_THE_IMMORTAL_MAEXXNA:
+            case ACHIEV_CRITERIA_THE_UNDYING_LOATHEB:
             case ACHIEV_CRITERIA_THE_IMMORTAL_LOATHEB:
+            case ACHIEV_CRITERIA_THE_UNDYING_THADDIUS:
             case ACHIEV_CRITERIA_THE_IMMORTAL_THADDIUS:
-                for (int i = 0; i < MAX_ENCOUNTERS; ++i)
-                    if (GetBossState(i) != DONE)
+            {
+                uint32 currentBoss;
+                switch (criteria_id)
+                {
+                    case ACHIEV_CRITERIA_THE_UNDYING_KELTHUZAD:
+                    case ACHIEV_CRITERIA_THE_IMMORTAL_KELTHUZAD:
+                        currentBoss = BOSS_KELTHUZAD;
+                        break;
+                    case ACHIEV_CRITERIA_THE_UNDYING_THE_FOUR_HORSEMEN:
+                    case ACHIEV_CRITERIA_THE_IMMORTAL_THE_FOUR_HORSEMEN:
+                        currentBoss = BOSS_HORSEMAN;
+                        break;
+                    case ACHIEV_CRITERIA_THE_UNDYING_MAEXXNA:
+                    case ACHIEV_CRITERIA_THE_IMMORTAL_MAEXXNA:
+                        currentBoss = BOSS_MAEXXNA;
+                        break;
+                    case ACHIEV_CRITERIA_THE_UNDYING_LOATHEB:
+                    case ACHIEV_CRITERIA_THE_IMMORTAL_LOATHEB:
+                        currentBoss = BOSS_LOATHEB;
+                        break;
+                    case ACHIEV_CRITERIA_THE_UNDYING_THADDIUS:
+                    case ACHIEV_CRITERIA_THE_IMMORTAL_THADDIUS:
+                        currentBoss = BOSS_THADDIUS;
+                        break;
+                    default:
+                        return false;
+                }
+
+                for (uint32 i = 0; i < MAX_ENCOUNTERS; ++i)
+                    if (i != currentBoss && GetBossState(i) != DONE)
                         return false;
 
                 return !GetPersistentData(PERSISTENT_DATA_IMMORTAL_FAIL);
+            }
             default:
                 return false;
         }