diff --git a/kmcos/types.py b/kmcos/types.py
index 118b67a1aa5a8d4d4e58e0b4b475f369ddfc7802..8bab71fa691b949721f24dd54e2cb34070b1afa9 100644
--- a/kmcos/types.py
+++ b/kmcos/types.py
@@ -589,7 +589,7 @@ class Project(object):
                               os.path.splitext(self.filename)[-1])
 
 
-    def save(self, filename=None, validate=True):
+    def save(self, filename="", validate=True):
         self.save_model(filename, validate)