diff --git a/src/nhp/data/raw_data/mitigators/ip/activity_avoidance/readmission_within_28_days.py b/src/nhp/data/raw_data/mitigators/ip/activity_avoidance/readmission_within_28_days.py
index 212e40f..3214029 100644
--- a/src/nhp/data/raw_data/mitigators/ip/activity_avoidance/readmission_within_28_days.py
+++ b/src/nhp/data/raw_data/mitigators/ip/activity_avoidance/readmission_within_28_days.py
@@ -43,7 +43,7 @@ def _readmission_within_28_days():
         .filter(F.col("last_episode_in_spell"))
         # remove well babies
         .filter(F.col("well_baby_ind") == "N")
-        .filter((F.isnull("sushrg") != "PB03Z") | F.col("sushrg"))
+        .filter((F.col("sushrg") != "PB03Z") | F.col("sushrg").isNull())
         .filter(~((F.col("tretspef") == "424") & (F.col("epitype") == "3")))
         #
         .withColumnRenamed("person_id_deid", "person_id")