diff --git a/propdict.py.orig b/propdict.py
index 172a74d..b39b5a3 100644
--- a/propdict.py.orig
+++ b/propdict.py
@@ -8,7 +8,9 @@ except NameError:
 class PropDict(dict):
     def __init__(self, srcs):
         dict.__init__(self)
-        self._sources = srcs
+        self._sources = list(srcs)
+        if len(self._sources) == 0:
+            self._sources = ['*']
 
     def set_source_preference(self, sources):
         """
@@ -54,6 +56,9 @@ class PropDict(dict):
     def _set_sources(self, val):
         if isinstance(val, basestring):
             raise TypeError("Need a sequence of sources")
+        val = list(val)
+        if len(val) == 0:
+            val = ['*']
         for i in val:
             if not isinstance(i, basestring):
                 raise TypeError("Sources need to be strings")