diff --git a/server/gameserver/global.h b/server/gameserver/global.h
index b692dd6..0a72459 100644
--- a/server/gameserver/global.h
+++ b/server/gameserver/global.h
@@ -12,6 +12,7 @@ class Global : public a8::Singleton<Global>
 
     static int g_nowtime;
     static ColliderComponent* last_collider;
+    int traversing_cell_creature_count = 0;
 };
 
 bool IsValidSlotId(int slot_id);
diff --git a/server/gameserver/gridcell.cc b/server/gameserver/gridcell.cc
index 58edb8b..de1b5c2 100644
--- a/server/gameserver/gridcell.cc
+++ b/server/gameserver/gridcell.cc
@@ -8,6 +8,7 @@
 #include "hero.h"
 #include "creature.h"
 #include "bullet.h"
+#include "global.h"
 
 GridCell::GridCell()
 {
@@ -32,6 +33,7 @@ void GridCell::TraverseHumanList(std::function<void (Human*, bool&)> func,
                               int room_idx,
                               bool& stop)
 {
+    ++Global::Instance()->traversing_cell_creature_count;
     for (Creature* c : creatures_[room_idx]) {
         if (!c->IsHuman()) {
             continue;
@@ -39,21 +41,26 @@ void GridCell::TraverseHumanList(std::function<void (Human*, bool&)> func,
         Human* hum = (Human*)c;
         func(hum, stop);
         if (stop) {
+            --Global::Instance()->traversing_cell_creature_count;
             return;
         }
     }
+    --Global::Instance()->traversing_cell_creature_count;
 }
 
 void GridCell::TraverseCreatures(std::function<void (Creature*, bool&)>& func,
                               int room_idx,
                               bool& stop)
 {
+    ++Global::Instance()->traversing_cell_creature_count;
     for (Creature* c : creatures_[room_idx]) {
         func(c, stop);
         if (stop) {
+            --Global::Instance()->traversing_cell_creature_count;
             return;
         }
     }
+    --Global::Instance()->traversing_cell_creature_count;
 }
 
 void GridCell::AddPermanentEntity(Entity* entity)
@@ -115,11 +122,21 @@ void GridCell::TraverseAllLayerEntityList(std::function<void (Entity*, bool&)>&
 
 void GridCell::AddCreature(Creature* c)
 {
+#ifdef DEBUG
+    if (Global::Instance()->traversing_cell_creature_count > 0) {
+        abort();
+    }
+#endif
     creatures_[c->room->GetRoomIdx()].insert(c);
 }
 
 void GridCell::RemoveCreature(Creature* c)
 {
+#ifdef DEBUG
+    if (Global::Instance()->traversing_cell_creature_count > 0) {
+        abort();
+    }
+#endif
     creatures_[c->room->GetRoomIdx()].erase(c);
 }