diff --git a/src/mac/carbon/toplevel.cpp b/src/mac/carbon/toplevel.cpp
index 2533d86b13..b4eb9c4467 100644
--- a/src/mac/carbon/toplevel.cpp
+++ b/src/mac/carbon/toplevel.cpp
@@ -374,6 +374,10 @@ void SetupMouseEvent( wxMouseEvent &wxevent , wxMacCarbonEvent &cEvent )
                     wxevent.m_wheelDelta = 1;
                     wxevent.m_linesPerAction = 1;
                 }
+                else
+                {
+                    wxevent.SetEventType( wxEVT_NULL );
+                }
             }
             break ;
         case kEventMouseEntered :