diff --git a/openmc/data/photon.py b/openmc/data/photon.py
index 25ded24cb..bc21b2e56 100644
--- a/openmc/data/photon.py
+++ b/openmc/data/photon.py
@@ -203,7 +203,9 @@ class AtomicRelaxation(EqualityMixin):
         for subshell, df in transitions.items():
             cv.check_value('subshell', subshell, _SUBSHELLS)
             cv.check_type('transitions', df, pd.DataFrame)
-        self._transitions = transitions
+        self._transitions = {
+            subshell: df.convert_dtypes() for subshell, df in transitions.items()
+        }
 
     @classmethod
     def from_ace(cls, ace):
diff --git a/openmc/tallies.py b/openmc/tallies.py
index 7b1ef0219..74d4722af 100644
--- a/openmc/tallies.py
+++ b/openmc/tallies.py
@@ -1982,7 +1982,7 @@ class Tally(IDManagerMixin):
 
         # Expand the columns into Pandas MultiIndices for readability
         if pd.__version__ >= '0.16':
-            columns = copy.deepcopy(df.columns.values)
+            columns = copy.deepcopy(list(df.columns.values))
 
             # Convert all elements in columns list to tuples
             for i, column in enumerate(columns):