diff --git a/rowers/dataprep.py b/rowers/dataprep.py
index 42efff8f..c6f8049d 100644
--- a/rowers/dataprep.py
+++ b/rowers/dataprep.py
@@ -124,6 +124,10 @@ from rq import Queue
 from rowers.datautils import rpetotss
 
 def rscore_approx(row):
+    if isinstance(row, pl.DataFrame):
+        row = {'rscore': row['rscore'][0]}
+    if isinstance(row, pl.Series):
+        row = {'rscore': row['rscore'][0]}
     if row['rscore'] > 0:
         return row['rscore']
     if row['rscore'] == 0: # pragma: no cover