diff --git a/piker/tsp/_anal.py b/piker/tsp/_anal.py
index ea78c46a..42c3aa6c 100644
--- a/piker/tsp/_anal.py
+++ b/piker/tsp/_anal.py
@@ -517,7 +517,7 @@ def with_dts(
 
     '''
     return df.with_columns([
-        pl.col(time_col).shift(1).suffix('_prev'),
+        pl.col(time_col).shift(1).name.suffix('_prev'),
         pl.col(time_col).diff().alias('s_diff'),
         pl.from_epoch(pl.col(time_col)).alias('dt'),
     ]).with_columns([
@@ -623,7 +623,7 @@ def detect_vlm_gaps(
 
 ) -> pl.DataFrame:
 
-    vnull: pl.DataFrame = w_dts.filter(
+    vnull: pl.DataFrame = df.filter(
         pl.col(col) == 0
     )
     return vnull