diff --git a/src/3rdparty/webkit/Source/JavaScriptCore/wtf/HashSet.h b/src/3rdparty/webkit/Source/JavaScriptCore/wtf/HashSet.h
index 82245f3..7298558 100644
--- a/src/3rdparty/webkit/Source/JavaScriptCore/wtf/HashSet.h
+++ b/src/3rdparty/webkit/Source/JavaScriptCore/wtf/HashSet.h
@@ -92,6 +92,17 @@ namespace WTF {
         friend void deleteAllValues<>(const HashSet&);
         friend void fastDeleteAllValues<>(const HashSet&);
 
+        // msvc2012 has trouble constructing a HashTableConstIteratorAdapter from a HashTableIterator
+        // despite the existence of a const_iterator cast method on the latter class.
+        pair<iterator, bool> iterator_const_cast(const pair<typename HashTableType::iterator, bool>& p)
+        {
+            // Spell out the full conversion chain for clarity, although any of the "hint"
+            // given by the alternatives below would have been enough.
+            return make_pair(iterator(HashTableType::const_iterator(p.first)), p.second);
+            //     return make_pair(iterator(p.first), p.second);
+            //     return make_pair(HashTableType::const_iterator(p.first), p.second);
+        }
+
         HashTableType m_impl;
     };
 
@@ -177,7 +188,7 @@ namespace WTF {
     template<typename T, typename U, typename V>
     inline pair<typename HashSet<T, U, V>::iterator, bool> HashSet<T, U, V>::add(const ValueType& value)
     {
-        return m_impl.add(value);
+        return iterator_const_cast(m_impl.add(value));
     }
 
     template<typename Value, typename HashFunctions, typename Traits>
@@ -186,7 +197,7 @@ namespace WTF {
     HashSet<Value, HashFunctions, Traits>::add(const T& value)
     {
         typedef HashSetTranslatorAdapter<ValueType, ValueTraits, T, HashTranslator> Adapter;
-        return m_impl.template addPassingHashCode<T, T, Adapter>(value, value);
+        return iterator_const_cast(m_impl.template addPassingHashCode<T, T, Adapter>(value, value));
     }
 
     template<typename T, typename U, typename V>