diff --git a/control/freqplot.py b/control/freqplot.py
index 961f499b3..2f0bcea28 100644
--- a/control/freqplot.py
+++ b/control/freqplot.py
@@ -2468,6 +2468,14 @@ def _determine_omega_vector(syslist, omega_in, omega_limits, omega_num,
     """
     omega_range_given = True
 
+    if omega_in is None:
+        for sys in syslist:
+            if isinstance(sys, FrequencyResponseData):
+                # FRD already has predetermined frequencies
+                if omega_in is not None and not np.all(omega_in == sys.omega):
+                    raise ValueError("List of FrequencyResponseData systems can only have a single frequency range between them")
+                omega_in = sys.omega
+
     if omega_in is None:
         if omega_limits is None:
             omega_range_given = False
diff --git a/control/tests/frd_test.py b/control/tests/frd_test.py
index 987121987..25ecc5e21 100644
--- a/control/tests/frd_test.py
+++ b/control/tests/frd_test.py
@@ -192,6 +192,8 @@ def testNyquist(self):
         # plt.savefig('/dev/null', format='svg')
         plt.figure(2)
         freqplot.nyquist(f1, f1.omega)
+        plt.figure(3)
+        freqplot.nyquist(f1)
         # plt.savefig('/dev/null', format='svg')
 
     @slycotonly