diff --git a/apps/openmw/mwmechanics/magiceffects.cpp b/apps/openmw/mwmechanics/magiceffects.cpp
index 52811084f..41d898ca8 100644
--- a/apps/openmw/mwmechanics/magiceffects.cpp
+++ b/apps/openmw/mwmechanics/magiceffects.cpp
@@ -85,6 +85,30 @@ namespace MWMechanics
         }
     }
 
+    MagicEffects& MagicEffects::operator+= (const MagicEffects& effects)
+    {
+        if (this==&effects)
+        {
+            MagicEffects temp (effects);
+            *this += temp;
+            return *this;
+        }
+
+        for (Collection::const_iterator iter (effects.Begin()); iter!=effects.End(); ++iter)
+        {
+            Collection::iterator result = mCollection.find (iter->first);
+
+            if (result!=mCollection.end())
+            {
+                result->second.mMagnitude += iter->second.mMagnitude;
+            }
+            else
+                mCollection.insert (*iter);
+        }
+
+        return *this;
+    }
+
     EffectParam MagicEffects::get (const EffectKey& key) const
     {
         Collection::const_iterator iter = mCollection.find (key);
diff --git a/apps/openmw/mwmechanics/magiceffects.hpp b/apps/openmw/mwmechanics/magiceffects.hpp
index d47101d45..26f78ec8a 100644
--- a/apps/openmw/mwmechanics/magiceffects.hpp
+++ b/apps/openmw/mwmechanics/magiceffects.hpp
@@ -69,6 +69,8 @@ namespace MWMechanics
 
             void add (const ESM::EffectList& list);
 
+            MagicEffects& operator+= (const MagicEffects& effects);
+
             EffectParam get (const EffectKey& key) const;
             ///< This function can safely be used for keys that are not present.