diff --git a/python/_cosmotool.pyx b/python/_cosmotool.pyx
index 83590b2..4da8716 100644
--- a/python/_cosmotool.pyx
+++ b/python/_cosmotool.pyx
@@ -333,7 +333,7 @@ def loadParallelGadget(list filename_list, bool loadPosition = True, bool loadVe
       data[i] = local_data
 #      data[i] = loadGadgetMulti(filenames[i].c_str(), -1, flags)
   
-  out_arrays = None    
+  out_arrays = []
   for i in xrange(num_files):
     if data[i] == <SimuData*>0:        
       out_arrays.append(None)