diff --git a/tests/test_core.py b/tests/test_core.py
index 16b8a4fe..e9978ec6 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -213,11 +213,11 @@ def nfreq_imp():
 @pytest.fixture(scope="module")
 def rao(ndof_imp, nfreq_imp):
     """Synthetic RAO transfer matrix."""
-    rao = np.empty([ndof_imp, ndof_imp, nfreq_imp], dtype=complex)
-    rao[0, 0, :] = [0+1j, 0+2j]
-    rao[1, 0, :] = [1+1j, 11+2j]
-    rao[0, 1, :] = [2+1j, 22+2j]
-    rao[1, 1, :] = [3+1j, 33+2j]
+    rao = np.empty([nfreq_imp, ndof_imp, ndof_imp], dtype=complex)
+    rao[:, 0, 0] = [0+1j, 0+2j]
+    rao[:, 1, 0] = [1+1j, 11+2j]
+    rao[:, 0, 1] = [2+1j, 22+2j]
+    rao[:, 1, 1] = [3+1j, 33+2j]
     return rao
 
 
@@ -576,7 +576,7 @@ def test_behavior(self,):
                 i in range(np.size(x)-1)], -1),
             [np.real(z[-1]) * np.real(x[-1])],
         ])
-        Z_mimo = wot.mimo_transfer_mat(np.reshape([z], [1,1,-1]), False)
+        Z_mimo = wot.mimo_transfer_mat(np.reshape([z], [-1, 1,1]), False)
         assert np.allclose(Z_mimo @ X, F)
 
 
diff --git a/wecopttool/core.py b/wecopttool/core.py
index d46c49de..c2f013bd 100644
--- a/wecopttool/core.py
+++ b/wecopttool/core.py
@@ -1963,8 +1963,7 @@ def force_from_impedance(
     --------
     force_from_rao_transfer_function,
     """
-    omega0 = np.expand_dims(omega, [1,2])
-    return force_from_rao_transfer_function(impedance*(1j*omega0), False)
+    return force_from_rao_transfer_function(impedance*(1j*omega), False)
 
 
 def force_from_waves(force_coeff: ArrayLike,
@@ -2000,7 +1999,7 @@ def inertia(
         Inertia matrix.
     """
     omega = np.expand_dims(frequency(f1, nfreq, False)*2*np.pi, [1,2])
-    inertia_matrix = np.expand_dims(inertia_matrix, -1)
+    inertia_matrix = np.expand_dims(inertia_matrix, 0)
     rao_transfer_function = -1*omega**2*inertia_matrix + 0j
     inertia_fun = force_from_rao_transfer_function(
         rao_transfer_function, False)