diff --git a/beat/backend/python/database.py b/beat/backend/python/database.py
index 2bc552e56242718fe1f44bc1409687ba81245bbf..3cd1aa116e71d883770fe92624587c3f9123719b 100755
--- a/beat/backend/python/database.py
+++ b/beat/backend/python/database.py
@@ -141,7 +141,7 @@ class Runner(object):
             os.makedirs(os.path.dirname(filename))
 
         with open(filename, 'wb') as f:
-            simplejson.dump(objs, f)
+            simplejson.dump(objs, f, cls=utils.NumpyJSONEncoder)
 
 
     def setup(self, filename, start_index=None, end_index=None, pack=True):