diff --git a/src/game/Achievements/AchievementMgr.cpp b/src/game/Achievements/AchievementMgr.cpp
index 881bc09ce..c30a53ac3 100644
--- a/src/game/Achievements/AchievementMgr.cpp
+++ b/src/game/Achievements/AchievementMgr.cpp
@@ -2163,9 +2163,7 @@ void AchievementMgr::CompletedAchievement(AchievementEntry const* achievement)
                     }
     }
 
-    // don't insert for ACHIEVEMENT_FLAG_REALM_FIRST_KILL since otherwise only the first group member would reach that achievement
-    // TODO: where do set this instead?
-    if (!(achievement->flags & ACHIEVEMENT_FLAG_REALM_FIRST_KILL))
+    if (achievement->flags & (ACHIEVEMENT_FLAG_REALM_FIRST_REACH | ACHIEVEMENT_FLAG_REALM_FIRST_KILL))
         sAchievementMgr->SetRealmCompleted(achievement);
 
     UpdateAchievementCriteria(ACHIEVEMENT_CRITERIA_TYPE_COMPLETE_ACHIEVEMENT, achievement->ID);
@@ -2307,6 +2305,35 @@ bool AchievementMgr::CanUpdateCriteria(AchievementCriteriaEntry const* criteria,
     return true;
 }
 
+bool AchievementGlobalMgr::IsRealmCompleted(AchievementEntry const* achievement) const
+{
+    auto itr = m_allCompletedAchievements.find(achievement->ID);
+    if (itr == m_allCompletedAchievements.end())
+        return false;
+
+    if (itr->second == std::chrono::system_clock::time_point::min())
+        return false;
+
+    if (itr->second == std::chrono::system_clock::time_point::max())
+        return true;
+
+    // Allow completing the realm first kill for entire minute after first person did it
+    // it may allow more than one group to achieve it (highly unlikely)
+    // but apparently this is how blizz handles it as well
+    if (achievement->flags & ACHIEVEMENT_FLAG_REALM_FIRST_KILL)
+        return (std::chrono::system_clock::now() - itr->second) > std::chrono::minutes(1);
+
+    return true;
+}
+
+void AchievementGlobalMgr::SetRealmCompleted(AchievementEntry const* achievement)
+{
+    if (IsRealmCompleted(achievement))
+        return;
+
+    m_allCompletedAchievements[achievement->ID] = std::chrono::system_clock::now();
+}
+
 //==========================================================
 void AchievementGlobalMgr::LoadAchievementCriteriaList()
 {
@@ -2628,6 +2655,14 @@ void AchievementGlobalMgr::LoadCompletedAchievements()
 
     QueryResult result = CharacterDatabase.Query("SELECT achievement FROM character_achievement GROUP BY achievement");
 
+    // Populate _allCompletedAchievements with all realm first achievement ids to make multithreaded access safer
+    // while it will not prevent races, it will prevent crashes that happen because std::unordered_map key was added
+    // instead the only potential race will happen on value associated with the key
+    for (uint32 i = 0; i < sAchievementStore.GetNumRows(); ++i)
+        if (AchievementEntry const* achievement = sAchievementStore.LookupEntry(i))
+            if (achievement->flags & (ACHIEVEMENT_FLAG_REALM_FIRST_REACH | ACHIEVEMENT_FLAG_REALM_FIRST_KILL))
+                m_allCompletedAchievements[achievement->ID] = std::chrono::system_clock::time_point::min();
+
     if (!result)
     {
         sLog->outString(">> Loaded 0 completed achievements. DB table `character_achievement` is empty.");
@@ -2655,7 +2690,7 @@ void AchievementGlobalMgr::LoadCompletedAchievements()
             continue;
         }
         else if (achievement->flags & (ACHIEVEMENT_FLAG_REALM_FIRST_REACH | ACHIEVEMENT_FLAG_REALM_FIRST_KILL))
-            m_allCompletedAchievements.insert(achievementId);
+            m_allCompletedAchievements[achievementId] =  std::chrono::system_clock::time_point::max();
     } while (result->NextRow());
 
     sLog->outString(">> Loaded %lu completed achievements in %u ms", (unsigned long)m_allCompletedAchievements.size(), GetMSTimeDiffToNow(oldMSTime));
diff --git a/src/game/Achievements/AchievementMgr.h b/src/game/Achievements/AchievementMgr.h
index 390a0cb58..ff5563943 100644
--- a/src/game/Achievements/AchievementMgr.h
+++ b/src/game/Achievements/AchievementMgr.h
@@ -8,6 +8,7 @@
 
 #include <map>
 #include <string>
+#include <chrono>
 
 #include "Common.h"
 #include <ace/Singleton.h>
@@ -348,15 +349,8 @@ class AchievementGlobalMgr
             return iter != m_criteriaDataMap.end() ? &iter->second : NULL;
         }
 
-        bool IsRealmCompleted(AchievementEntry const* achievement) const
-        {
-            return m_allCompletedAchievements.find(achievement->ID) != m_allCompletedAchievements.end();
-        }
-
-        void SetRealmCompleted(AchievementEntry const* achievement)
-        {
-            m_allCompletedAchievements.insert(achievement->ID);
-        }
+        bool IsRealmCompleted(AchievementEntry const* achievement) const;
+        void SetRealmCompleted(AchievementEntry const* achievement);
 
         void LoadAchievementCriteriaList();
         void LoadAchievementCriteriaData();
@@ -375,7 +369,7 @@ class AchievementGlobalMgr
         // store achievements by referenced achievement id to speed up lookup
         AchievementListByReferencedId m_AchievementListByReferencedId;
 
-        typedef std::set<uint32> AllCompletedAchievements;
+        typedef UNORDERED_MAP<uint32 /*achievementId*/, std::chrono::system_clock::time_point /*completionTime*/> AllCompletedAchievements;
         AllCompletedAchievements m_allCompletedAchievements;
 
         AchievementRewards m_achievementRewards;