diff --git a/pycox/evaluation/eval_surv.py b/pycox/evaluation/eval_surv.py
index 5e16753..9ad5d8c 100644
--- a/pycox/evaluation/eval_surv.py
+++ b/pycox/evaluation/eval_surv.py
@@ -33,7 +33,7 @@ def __init__(self, surv, durations, events, censor_surv=None, censor_durations=N
         self.censor_surv = censor_surv
         self.censor_durations = censor_durations
         self.steps = steps
-        assert pd.Series(self.index_surv).is_monotonic
+        assert pd.Series(self.index_surv).is_monotonic_increasing
 
     @property
     def censor_surv(self):
diff --git a/pycox/models/cox_time.py b/pycox/models/cox_time.py
index 12b9cde..e663d67 100644
--- a/pycox/models/cox_time.py
+++ b/pycox/models/cox_time.py
@@ -94,7 +94,7 @@ def compute_expg_at_risk(ix, t):
                  [self.duration_col]
                  .loc[lambda x: x <= max_duration]
                  .drop_duplicates(keep='first'))
-        at_risk_sum = (pd.Series([compute_expg_at_risk(ix, t) for ix, t in times.iteritems()],
+        at_risk_sum = (pd.Series([compute_expg_at_risk(ix, t) for ix, t in times.items()],
                                  index=times.values)
                        .rename('at_risk_sum'))
         events = (df
diff --git a/pycox/models/data.py b/pycox/models/data.py
index a89b431..52fbafd 100644
--- a/pycox/models/data.py
+++ b/pycox/models/data.py
@@ -35,7 +35,7 @@ def make_at_risk_dict(durations):
     allidx = durations.index.values
     keys = durations.drop_duplicates(keep='first')
     at_risk_dict = dict()
-    for ix, t in keys.iteritems():
+    for ix, t in keys.items():
         at_risk_dict[t] = allidx[ix:]
     return at_risk_dict