diff --git a/apps/openmw/mwworld/containerstore.cpp b/apps/openmw/mwworld/containerstore.cpp
index dcddc333b0..ee1b620cd7 100644
--- a/apps/openmw/mwworld/containerstore.cpp
+++ b/apps/openmw/mwworld/containerstore.cpp
@@ -45,7 +45,7 @@ MWWorld::ContainerStoreIterator MWWorld::ContainerStore::end()
     return ContainerStoreIterator (this);
 }
 
-bool MWWorld::ContainerStore::stacks(const Ptr& ptr1, const Ptr& ptr2) const
+bool MWWorld::ContainerStore::stacks(const Ptr& ptr1, const Ptr& ptr2)
 {
     /// \todo add current weapon/armor health, remaining lockpick/repair uses, current enchantment charge here as soon as they are implemented
     if (  ptr1.mCellRef->refID == ptr2.mCellRef->refID
diff --git a/apps/openmw/mwworld/containerstore.hpp b/apps/openmw/mwworld/containerstore.hpp
index f0e9d7e4ab..3cb3f3bdc5 100644
--- a/apps/openmw/mwworld/containerstore.hpp
+++ b/apps/openmw/mwworld/containerstore.hpp
@@ -78,7 +78,7 @@ namespace MWWorld
             void addImpl (const Ptr& ptr);
             ///< Add the item to this container (no stacking)
 
-            virtual bool stacks (const Ptr& ptr1, const Ptr& ptr2) const;
+            virtual bool stacks (const Ptr& ptr1, const Ptr& ptr2);
             ///< @return true if the two specified objects can stack with each other
             /// @note ptr1 is the item that is already in this container
 
diff --git a/apps/openmw/mwworld/inventorystore.cpp b/apps/openmw/mwworld/inventorystore.cpp
index 6cf35ac644..3e535793c0 100644
--- a/apps/openmw/mwworld/inventorystore.cpp
+++ b/apps/openmw/mwworld/inventorystore.cpp
@@ -201,7 +201,7 @@ void MWWorld::InventoryStore::autoEquip (const MWMechanics::NpcStats& stats)
     }
 }
 
-bool MWWorld::InventoryStore::stacks(const Ptr& ptr1, const Ptr& ptr2) const
+bool MWWorld::InventoryStore::stacks(const Ptr& ptr1, const Ptr& ptr2)
 {
     bool canStack = MWWorld::ContainerStore::stacks(ptr1, ptr2);
     if (!canStack)
@@ -211,7 +211,7 @@ bool MWWorld::InventoryStore::stacks(const Ptr& ptr1, const Ptr& ptr2) const
     for (TSlots::const_iterator iter (mSlots.begin());
         iter!=mSlots.end(); ++iter)
     {
-        if (ptr1 == **iter)
+        if (*iter != end() && ptr1 == **iter)
             return false;
     }
 
diff --git a/apps/openmw/mwworld/inventorystore.hpp b/apps/openmw/mwworld/inventorystore.hpp
index 4162c7e2e8..05fc651ee7 100644
--- a/apps/openmw/mwworld/inventorystore.hpp
+++ b/apps/openmw/mwworld/inventorystore.hpp
@@ -67,7 +67,7 @@ namespace MWWorld
 
         protected:
 
-            virtual bool stacks (const Ptr& ptr1, const Ptr& ptr2) const;
+            virtual bool stacks (const Ptr& ptr1, const Ptr& ptr2);
             ///< @return true if the two specified objects can stack with each other
             /// @note ptr1 is the item that is already in this container