diff --git a/openmc/deplete/results_list.py b/openmc/deplete/results_list.py
index 390724fc89..02e55f8f88 100644
--- a/openmc/deplete/results_list.py
+++ b/openmc/deplete/results_list.py
@@ -243,6 +243,9 @@ class ResultsList(list):
         will be at most one past the point in time requested, but only
         according to tolerances requested.
 
+        Passing ``atol=math.inf`` and ``rtol=math.inf`` will return
+        the closest index to the requested point.
+
         Parameters
         ----------
         time : float
@@ -251,10 +254,9 @@ class ResultsList(list):
             Units on ``time``. Default: days
         atol : float, optional
             Absolute tolerance (in ``time_units``) if ``time`` is not
-            found. A value of ``None`` is converted to infinity.
+            found.
         rtol : float, optional
-            Relative tolerance if ``time`` is not found. A value of
-            ``None`` is converted to infinity.
+            Relative tolerance if ``time`` is not found.
 
         Returns
         -------
@@ -262,14 +264,8 @@ class ResultsList(list):
 
         """
         check_type("time", time, numbers.Real)
-        if atol is not None:
-            check_type("atol", atol, numbers.Real)
-        else:
-            atol = math.inf
-        if rtol is not None:
-            check_type("rtol", rtol, numbers.Real)
-        else:
-            rtol = math.inf
+        check_type("atol", atol, numbers.Real)
+        check_type("rtol", rtol, numbers.Real)
 
         times = self.get_times(time_units)
 
diff --git a/tests/unit_tests/test_deplete_resultslist.py b/tests/unit_tests/test_deplete_resultslist.py
index c96108cfd2..392d5d0d5c 100644
--- a/tests/unit_tests/test_deplete_resultslist.py
+++ b/tests/unit_tests/test_deplete_resultslist.py
@@ -1,6 +1,7 @@
 """Tests the ResultsList class"""
 
 from pathlib import Path
+from math import inf
 
 import numpy as np
 import pytest
@@ -110,12 +111,12 @@ def test_get_steps(unit):
             target = value + mult * offset
             # Compare using absolute and relative tolerances
             actual = results.get_step_where(
-                target, time_units=unit, atol=offset * 2, rtol=None)
+                target, time_units=unit, atol=offset * 2, rtol=inf)
             assert actual == expected, (
                 target, times[actual], times[expected], offset)
 
             actual = results.get_step_where(
-                target, time_units=unit, atol=None, rtol=offset / value)
+                target, time_units=unit, atol=inf, rtol=offset / value)
             assert actual == expected, (
                 target, times[actual], times[expected], offset)
         # Check that the lower index is returned for the exact mid-point
@@ -126,5 +127,5 @@ def test_get_steps(unit):
 
     # Shoot way over with no tolerance -> just give closest value
     actual = results.get_step_where(
-        times[-1] * 100, time_units=unit, atol=None, rtol=None)
+        times[-1] * 100, time_units=unit, atol=inf, rtol=inf)
     assert actual == times.size - 1