diff --git a/apps/openmw/mwworld/class.cpp b/apps/openmw/mwworld/class.cpp
index d3d1aff49..ffe81a4ac 100644
--- a/apps/openmw/mwworld/class.cpp
+++ b/apps/openmw/mwworld/class.cpp
@@ -139,7 +139,7 @@ namespace MWWorld
 
     float Class::getRemainingUsageTime (const Ptr& ptr) const
     {
-        throw std::runtime_error ("class does not support time-based uses");
+        return -1;
     }
 
     std::string Class::getScript (const Ptr& ptr) const
diff --git a/apps/openmw/mwworld/class.hpp b/apps/openmw/mwworld/class.hpp
index 2db293e68..cb6690a46 100644
--- a/apps/openmw/mwworld/class.hpp
+++ b/apps/openmw/mwworld/class.hpp
@@ -162,7 +162,7 @@ namespace MWWorld
 
             virtual float getRemainingUsageTime (const Ptr& ptr) const;
             ///< Returns the remaining duration of the object, such as an equippable light
-            /// source. (default implementation: throw an exception)
+            /// source. (default implementation: -1, i.e. infinite)
 
             virtual std::string getScript (const Ptr& ptr) const;
             ///< Return name of the script attached to ptr (default implementation: return an empty
diff --git a/apps/openmw/mwworld/containerstore.cpp b/apps/openmw/mwworld/containerstore.cpp
index d1d16ee01..3797e6922 100644
--- a/apps/openmw/mwworld/containerstore.cpp
+++ b/apps/openmw/mwworld/containerstore.cpp
@@ -109,6 +109,8 @@ bool MWWorld::ContainerStore::stacks(const Ptr& ptr1, const Ptr& ptr2)
         && ptr1.getCellRef().mOwner == ptr2.getCellRef().mOwner
         && ptr1.getCellRef().mSoul == ptr2.getCellRef().mSoul
 
+        && ptr1.getClass().getRemainingUsageTime(ptr1) == ptr2.getClass().getRemainingUsageTime(ptr2)
+
         && cls1.getScript(ptr1) == cls2.getScript(ptr2)
 
         // item that is already partly used up never stacks