diff --git a/CodeEntropy/entropy/nodes/vibrational.py b/CodeEntropy/entropy/nodes/vibrational.py
index f6ed2f8..c663421 100644
--- a/CodeEntropy/entropy/nodes/vibrational.py
+++ b/CodeEntropy/entropy/nodes/vibrational.py
@@ -323,7 +323,7 @@ def _compute_force_torque_entropy(
             EntropyPair containing translational entropy (from force covariance) and
             rotational entropy (from torque covariance).
         """
-        if fmat is None or tmat is None:
+        if fmat is None and tmat is None:
             return EntropyPair(trans=0.0, rot=0.0)
 
         f = self._mat_ops.filter_zero_rows_columns(
@@ -333,7 +333,7 @@ def _compute_force_torque_entropy(
             np.asarray(tmat), atol=self._zero_atol
         )
 
-        if f.size == 0 or t.size == 0:
+        if f.size == 0 and t.size == 0:
             return EntropyPair(trans=0.0, rot=0.0)
 
         s_trans = ve.vibrational_entropy_calculation(
diff --git a/tests/unit/CodeEntropy/entropy/nodes/test_vibrational_node.py b/tests/unit/CodeEntropy/entropy/nodes/test_vibrational_node.py
index e352b84..d8e5ce5 100644
--- a/tests/unit/CodeEntropy/entropy/nodes/test_vibrational_node.py
+++ b/tests/unit/CodeEntropy/entropy/nodes/test_vibrational_node.py
@@ -321,7 +321,7 @@ def test_compute_force_torque_entropy_returns_zero_when_missing_matrix(shared_gr
     node = VibrationalEntropyNode()
     ve = MagicMock()
     pair = node._compute_force_torque_entropy(
-        ve=ve, temp=298.0, fmat=None, tmat=np.eye(3), flexible=0, highest=True
+        ve=ve, temp=298.0, fmat=None, tmat=None, flexible=0, highest=True
     )
     assert pair == EntropyPair(trans=0.0, rot=0.0)