diff --git a/src/server/game/Instances/InstanceScript.cpp b/src/server/game/Instances/InstanceScript.cpp
index 16eedc7e9f0..bce1c51b176 100644
--- a/src/server/game/Instances/InstanceScript.cpp
+++ b/src/server/game/Instances/InstanceScript.cpp
@@ -624,7 +624,7 @@ void InstanceScript::SendEncounterUnit(uint32 type, Unit* unit /*= NULL*/, uint8
         case ENCOUNTER_FRAME_UPDATE_PRIORITY:
             if (!unit)
                 return;
-            data << unit->GetPackGUID();
+            data.appendPackGUID(unit->GetGUID());
             data << uint8(param1);
             break;
         case ENCOUNTER_FRAME_ADD_TIMER: