diff --git a/buildbot/master.cfg b/buildbot/master.cfg
index 82e87ca4..aa102ab3 100644
--- a/buildbot/master.cfg
+++ b/buildbot/master.cfg
@@ -135,8 +135,9 @@ def makeFactory(port, buildType='buildOnly', pyVer='2.7'):
     method = None
     clean = ''
     
-    # Since the wx build doesn't have good dependency checking on MSW, clean first
-    if port in ['win32', 'win64']:
+    # Since the wx build doesn't have good dependency checking on MSW, clean first.
+    # Generation of dependency files is turned off for universal builds, so clean on osx too.
+    if port in ['win32', 'win64', 'osx']:
         clean = 'clean'  
         
     # Start from a clean build tree for the daily builds