diff --git a/potsdb/client.py b/potsdb/client.py
index b90199f..8bdde37 100644
--- a/potsdb/client.py
+++ b/potsdb/client.py
@@ -143,6 +143,8 @@ def log(self, name, val, **tags):
                 return  # discard duplicate metrics
             else:
                 _last_metrics.add(unique_str)
+            if _last_timestamp == None:
+                _last_timestamp = timestamp
         else:
             _last_timestamp = timestamp
             _last_metrics.clear()