diff --git a/libs/ardour/wscript b/libs/ardour/wscript
index b4d4d96f62..f8e5314f7b 100644
--- a/libs/ardour/wscript
+++ b/libs/ardour/wscript
@@ -394,7 +394,7 @@ def build(bld):
     if bld.env['VST_SUPPORT']:
         obj.source += [ 'vst_plugin.cc', 'session_vst.cc' ]
         obj.includes += [ '../fst' ]
-        obj.cxxflags += [ '-DVST_SUPPORT' ]
+        obj.defines += [ '-DVST_SUPPORT' ]
 
     if bld.env['COREAUDIO']:
         obj.source += [ 'coreaudiosource.cc', 'caimportable.cc' ]