diff --git a/include/osgDB/ObjectCache b/include/osgDB/ObjectCache
index d6179b51a..01b3f0581 100644
--- a/include/osgDB/ObjectCache
+++ b/include/osgDB/ObjectCache
@@ -68,9 +68,15 @@ class OSGDB_EXPORT ObjectCache : public osg::Referenced
 
         virtual ~ObjectCache();
 
-        typedef std::pair<osg::ref_ptr<osg::Object>, double >           ObjectTimeStampPair;
         typedef std::pair<std::string, osg::ref_ptr<const osgDB::Options> >   FileNameOptionsPair;
-        typedef std::map<FileNameOptionsPair, ObjectTimeStampPair >     ObjectCacheMap;
+
+        class ClassComp {
+        public:
+            bool operator() (const ObjectCache::FileNameOptionsPair& lhs, const ObjectCache::FileNameOptionsPair& rhs);
+        };
+
+        typedef std::pair<osg::ref_ptr<osg::Object>, double >           ObjectTimeStampPair;
+        typedef std::map<FileNameOptionsPair, ObjectTimeStampPair, ClassComp>     ObjectCacheMap;
 
         ObjectCacheMap                          _objectCache;
         OpenThreads::Mutex                      _objectCacheMutex;
diff --git a/src/osgDB/ObjectCache.cpp b/src/osgDB/ObjectCache.cpp
index 872172395..48acc1b88 100644
--- a/src/osgDB/ObjectCache.cpp
+++ b/src/osgDB/ObjectCache.cpp
@@ -16,6 +16,11 @@
 
 using namespace osgDB;
 
+bool ObjectCache::ClassComp::operator() (const ObjectCache::FileNameOptionsPair& lhs, const ObjectCache::FileNameOptionsPair& rhs)
+{
+    return lhs.first < rhs.first || *lhs.second < *rhs.second;
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////
 //
 // ObjectCache