diff --git a/include/wx/sizer.h b/include/wx/sizer.h
index ff462469b2..41da10945d 100644
--- a/include/wx/sizer.h
+++ b/include/wx/sizer.h
@@ -125,6 +125,10 @@ public:
 
     wxSizerFlags& Border(int direction, int borderInPixels)
     {
+        wxCHECK_MSG( !(direction & ~wxALL), *this,
+                     wxS("direction must be a combination of wxDirection enum "
+                         "values.") );
+
         m_flags &= ~wxALL;
         m_flags |= direction;