diff --git a/piker/fsp/_engine.py b/piker/fsp/_engine.py
index f5af2ac2..37852cfc 100644
--- a/piker/fsp/_engine.py
+++ b/piker/fsp/_engine.py
@@ -188,7 +188,7 @@ async def fsp_compute(
 
     history_by_field['time'] = src_time[-len(history_by_field):]
 
-    history['time'] = src.array['time']
+    history_output['time'] = src.array['time']
 
     # TODO: XXX:
     # THERE'S A BIG BUG HERE WITH THE `index` field since we're