diff --git a/causal_testing/testing/estimators.py b/causal_testing/testing/estimators.py
index 3920e1f2..ffe76387 100644
--- a/causal_testing/testing/estimators.py
+++ b/causal_testing/testing/estimators.py
@@ -823,7 +823,7 @@ def estimate_hazard_ratio(self):
 
         #  IPCW step 4: Use these weights in a weighted analysis of the outcome model
         # Estimate the KM graph and IPCW hazard ratio using Cox regression.
-        cox_ph = CoxPHFitter()
+        cox_ph = CoxPHFitter(alpha=self.alpha)
         cox_ph.fit(
             df=preprocessed_data,
             duration_col="tout",