diff -r 055af17f7225 src/devices/wifi/interference-helper.cc
--- a/src/devices/wifi/interference-helper.cc	Thu Aug 13 13:39:23 2009 +0200
+++ b/src/devices/wifi/interference-helper.cc	Thu Aug 13 13:56:48 2009 +0200
@@ -460,7 +460,11 @@
           i++;
           continue;
         }
-      if (event->Overlaps ((*i)->GetStartTime ())) 
+      if ((*i)->Overlaps (event->GetStartTime ())) 
+        {
+          noiseInterference += (*i)->GetRxPowerW ();
+        }
+      else if (event->Overlaps ((*i)->GetStartTime ())) 
         {
           ni->push_back (NiChange ((*i)->GetStartTime (), (*i)->GetRxPowerW ()));
         }
@@ -468,10 +472,6 @@
         {
           ni->push_back (NiChange ((*i)->GetEndTime (), -(*i)->GetRxPowerW ()));
         }
-      if ((*i)->Overlaps (event->GetStartTime ())) 
-        {
-          noiseInterference += (*i)->GetRxPowerW ();
-        }
       i++;
     }
   ni->push_back (NiChange (event->GetStartTime (), noiseInterference));