diff --git a/seinflux.py b/seinflux.py
index 9773117..8e034e8 100644
--- a/seinflux.py
+++ b/seinflux.py
@@ -381,12 +381,13 @@ class SEHistory(InfluxDBWrapper):
         :param ts: the time or None when now
         """
         flag = value is not None
-        try:
-            previns, prevts = self.get_instrument(stream, ts, **tags)
-            if prevts is not None and (previns is None or (ts or 1e10) < prevts):
-                ts = prevts + 0.001
-        except Exception as e:
-            print(f'Exception in get_instrument {e!r}')
+        if flag:
+            try:
+                previns, prevts = self.get_instrument(stream, ts, **tags)
+                if prevts is not None and (previns is None or (ts or 1e10) < prevts):
+                    ts = prevts + 0.001
+            except Exception as e:
+                print(f'Exception in get_instrument {e!r}')
         tags['stream'] = stream
         if flag:
             tags['instrument'] = value