diff --git a/aosstower/level_b1/nc.py b/aosstower/level_b1/nc.py
index 5b9c96d2f19fe2d2e9a52b8bce0f3f8eae1eb51a..84e36b81dcb39f6fc3665f7dc33aff879019955e 100644
--- a/aosstower/level_b1/nc.py
+++ b/aosstower/level_b1/nc.py
@@ -101,11 +101,12 @@ def create_giant_netcdf(input_files, output_fn, zlib, chunk_size,
 
     # average the values
     if summary:
-        frame = summary_over_interval(new_frame, interval_width).fillna(np.nan)
+        frame = summary_over_interval(new_frame, interval_width)
     else:
-        frame = new_frame.resample(interval_width, closed='right', loffset=interval_width).mean().fillna(np.nan)
+        frame = new_frame.resample(interval_width, closed='right', loffset=interval_width).mean()
         frame['wind_dir'] = calc.wind_vector_degrees(frame['wind_east'], frame['wind_north'])
         frame['gust'] = new_frame['gust'].resample(interval_width, closed='right', loffset=interval_width).max()
+    frame = frame.fillna(np.nan)
 
     if start and end:
         frame = frame[start.strftime('%Y-%m-%d %H:%M:%S'): end.strftime('%Y-%m-%d %H:%M:%S')]