diff --git a/src/simulator/scheduler-map.cc b/src/simulator/scheduler-map.cc
index 0c38f87d1..ac2054d5b 100644
--- a/src/simulator/scheduler-map.cc
+++ b/src/simulator/scheduler-map.cc
@@ -49,16 +49,20 @@ SchedulerMap::~SchedulerMap ()
  * - transitivity: f(x,y) and f(y,z) => f(x,z)
  */
 bool
-SchedulerMap::EventKeyCompare::operator () (struct EventKey a, struct EventKey b)
+SchedulerMap::EventKeyCompare::operator () (struct EventKey const&a, struct EventKey const&b)
 {
   if (a.m_ns < b.m_ns) 
     {
       return true;
     } 
-  else if (a.m_ns == b.m_ns && a.m_uid < b.m_uid) 
+  else if (a.m_ns > b.m_ns)
+    {
+      return false;
+    } 
+  else if (a.m_uid < b.m_uid)
     {
       return true;
-    } 
+    }
   else 
     {
       return false;
diff --git a/src/simulator/scheduler-map.h b/src/simulator/scheduler-map.h
index 1a549de6c..4b32c34de 100644
--- a/src/simulator/scheduler-map.h
+++ b/src/simulator/scheduler-map.h
@@ -47,7 +47,7 @@ private:
 
   class EventKeyCompare {
   public:
-    bool operator () (struct EventKey a, struct EventKey b);
+    bool operator () (struct EventKey const&a, struct EventKey const&b);
   };
 
   typedef std::map<Scheduler::EventKey, EventImpl*, SchedulerMap::EventKeyCompare> EventMap;