diff --git a/apps/openmw/mwclass/npc.cpp b/apps/openmw/mwclass/npc.cpp
index 7238ad453..82dcf052b 100644
--- a/apps/openmw/mwclass/npc.cpp
+++ b/apps/openmw/mwclass/npc.cpp
@@ -1201,7 +1201,7 @@ namespace MWClass
             return ref->mBase->mNpdt12.mGold;
     }
 
-    bool Npc::isClass(const MWWorld::Ptr& ptr, const std::string &className) const
+    bool Npc::isClass(const MWWorld::ConstPtr& ptr, const std::string &className) const
     {
         return Misc::StringUtils::ciEqual(ptr.get<ESM::NPC>()->mBase->mClass, className);
     }
diff --git a/apps/openmw/mwclass/npc.hpp b/apps/openmw/mwclass/npc.hpp
index 946276876..f86eeb8ff 100644
--- a/apps/openmw/mwclass/npc.hpp
+++ b/apps/openmw/mwclass/npc.hpp
@@ -150,7 +150,7 @@ namespace MWClass
 
             virtual int getBaseGold(const MWWorld::ConstPtr& ptr) const;
 
-            virtual bool isClass(const MWWorld::Ptr& ptr, const std::string &className) const;
+            virtual bool isClass(const MWWorld::ConstPtr& ptr, const std::string &className) const;
 
             virtual bool canSwim (const MWWorld::ConstPtr &ptr) const;
 
diff --git a/apps/openmw/mwworld/class.cpp b/apps/openmw/mwworld/class.cpp
index c4cef4a8b..bf5fdebb8 100644
--- a/apps/openmw/mwworld/class.cpp
+++ b/apps/openmw/mwworld/class.cpp
@@ -404,7 +404,7 @@ namespace MWWorld
         throw std::runtime_error("class does not support base gold");
     }
 
-    bool Class::isClass(const MWWorld::Ptr& ptr, const std::string &className) const
+    bool Class::isClass(const MWWorld::ConstPtr& ptr, const std::string &className) const
     {
         return false;
     }
diff --git a/apps/openmw/mwworld/class.hpp b/apps/openmw/mwworld/class.hpp
index fd2c1da8e..5a9a49d5a 100644
--- a/apps/openmw/mwworld/class.hpp
+++ b/apps/openmw/mwworld/class.hpp
@@ -322,7 +322,7 @@ namespace MWWorld
 
             virtual int getBaseGold(const MWWorld::ConstPtr& ptr) const;
 
-            virtual bool isClass(const MWWorld::Ptr& ptr, const std::string &className) const;
+            virtual bool isClass(const MWWorld::ConstPtr& ptr, const std::string &className) const;
 
             /// 0 = nothing, 1 = opening, 2 = closing
             virtual int getDoorState (const MWWorld::Ptr &ptr) const;