diff --git a/apps/openmw/mwclass/creature.cpp b/apps/openmw/mwclass/creature.cpp
index 2483f2a7e..26bb45ea3 100644
--- a/apps/openmw/mwclass/creature.cpp
+++ b/apps/openmw/mwclass/creature.cpp
@@ -554,9 +554,9 @@ namespace MWClass
             return 0;
     }
 
-    bool Creature::isPersistent(const MWWorld::Ptr &actor) const
+    bool Creature::isPersistent(const MWWorld::ConstPtr &actor) const
     {
-        MWWorld::LiveCellRef<ESM::Creature>* ref = actor.get<ESM::Creature>();
+        const MWWorld::LiveCellRef<ESM::Creature>* ref = actor.get<ESM::Creature>();
         return ref->mBase->mPersistent;
     }
 
diff --git a/apps/openmw/mwclass/creature.hpp b/apps/openmw/mwclass/creature.hpp
index 72305a1d8..2299e655c 100644
--- a/apps/openmw/mwclass/creature.hpp
+++ b/apps/openmw/mwclass/creature.hpp
@@ -88,7 +88,7 @@ namespace MWClass
 
             virtual int getServices (const MWWorld::Ptr& actor) const;
 
-            virtual bool isPersistent (const MWWorld::Ptr& ptr) const;
+            virtual bool isPersistent (const MWWorld::ConstPtr& ptr) const;
 
             virtual std::string getSoundIdFromSndGen(const MWWorld::Ptr &ptr, const std::string &name) const;
 
diff --git a/apps/openmw/mwclass/npc.cpp b/apps/openmw/mwclass/npc.cpp
index 0e9618608..d05b0235e 100644
--- a/apps/openmw/mwclass/npc.cpp
+++ b/apps/openmw/mwclass/npc.cpp
@@ -419,9 +419,9 @@ namespace MWClass
         renderingInterface.getObjects().insertNPC(ptr);
     }
 
-    bool Npc::isPersistent(const MWWorld::Ptr &actor) const
+    bool Npc::isPersistent(const MWWorld::ConstPtr &actor) const
     {
-        MWWorld::LiveCellRef<ESM::NPC>* ref = actor.get<ESM::NPC>();
+        const MWWorld::LiveCellRef<ESM::NPC>* ref = actor.get<ESM::NPC>();
         return ref->mBase->mPersistent;
     }
 
diff --git a/apps/openmw/mwclass/npc.hpp b/apps/openmw/mwclass/npc.hpp
index 3dfb0b96e..8dd78f484 100644
--- a/apps/openmw/mwclass/npc.hpp
+++ b/apps/openmw/mwclass/npc.hpp
@@ -119,7 +119,7 @@ namespace MWClass
 
             virtual int getServices (const MWWorld::Ptr& actor) const;
 
-            virtual bool isPersistent (const MWWorld::Ptr& ptr) const;
+            virtual bool isPersistent (const MWWorld::ConstPtr& ptr) const;
 
             virtual std::string getSoundIdFromSndGen(const MWWorld::Ptr &ptr, const std::string &name) const;
 
diff --git a/apps/openmw/mwworld/class.cpp b/apps/openmw/mwworld/class.cpp
index a07c94a0c..b4861c85f 100644
--- a/apps/openmw/mwworld/class.cpp
+++ b/apps/openmw/mwworld/class.cpp
@@ -241,7 +241,7 @@ namespace MWWorld
         return *iter->second;
     }
 
-    bool Class::isPersistent(const Ptr &ptr) const
+    bool Class::isPersistent(const ConstPtr &ptr) const
     {
         throw std::runtime_error ("class does not support persistence");
     }
diff --git a/apps/openmw/mwworld/class.hpp b/apps/openmw/mwworld/class.hpp
index 4fc0c96ec..3cf4326c8 100644
--- a/apps/openmw/mwworld/class.hpp
+++ b/apps/openmw/mwworld/class.hpp
@@ -277,7 +277,7 @@ namespace MWWorld
 
             virtual float getWeight (const MWWorld::ConstPtr& ptr) const;
 
-            virtual bool isPersistent (const MWWorld::Ptr& ptr) const;
+            virtual bool isPersistent (const MWWorld::ConstPtr& ptr) const;
 
             virtual bool isKey (const MWWorld::ConstPtr& ptr) const { return false; }