diff --git a/site_scons/site_init.py b/site_scons/site_init.py
index cfe68e7..d1412f0 100644
--- a/site_scons/site_init.py
+++ b/site_scons/site_init.py
@@ -2,13 +2,16 @@
 # Eryn Wells <eryn@erynwells.me>
 
 
-def do_sconscript(env, src_dir, out_dir):
+def do_sconscript(env, src_dir, out_dir=None):
     '''
     Look for a SConscript file in `src_dir` and run it. Return any result.
     '''
     sconscript = src_dir.File('SConscript')
     print 'Reading {}'.format(sconscript)
-    return env.SConscript(sconscript, {'env': env}, variant_dir=out_dir)
+    kwargs = {}
+    if out_dir:
+        kwargs['variant_dir'] = out_dir
+    return env.SConscript(sconscript, {'env': env}, **kwargs)
 
 #
 # Argument utils