diff --git a/control/statesp.py b/control/statesp.py
index e3e491690..abd55ad15 100644
--- a/control/statesp.py
+++ b/control/statesp.py
@@ -288,7 +288,7 @@ def __init__(self, *args, **kwargs):
         if len(args) == 4:
             if 'dt' in kwargs:
                 dt = kwargs['dt']
-            elif self.is_static_gain():
+            elif self._isstatic():
                 dt = None
             else:
                 dt = config.defaults['control.default_dt']
@@ -300,7 +300,7 @@ def __init__(self, *args, **kwargs):
             try:
                 dt = args[0].dt
             except AttributeError:
-                if self.is_static_gain():
+                if self._isstatic():
                     dt = None
                 else:
                     dt = config.defaults['control.default_dt']
@@ -1213,7 +1213,7 @@ def dcgain(self):
             gain = np.tile(np.nan, (self.noutputs, self.ninputs))
         return np.squeeze(gain)
 
-    def is_static_gain(self):
+    def _isstatic(self):
         """True if and only if the system has no dynamics, that is,
         if A and B are zero. """
         return not np.any(self.A) and not np.any(self.B)
diff --git a/control/tests/statesp_test.py b/control/tests/statesp_test.py
index 9030b850a..1c76efbc0 100644
--- a/control/tests/statesp_test.py
+++ b/control/tests/statesp_test.py
@@ -383,7 +383,7 @@ def test_freq_resp(self):
             mag, phase, omega = sys.freqresp(true_omega)
             np.testing.assert_almost_equal(mag, true_mag)
 
-    def test_is_static_gain(self):
+    def test__isstatic(self):
         A0 = np.zeros((2,2))
         A1 = A0.copy()
         A1[0,1] = 1.1
@@ -394,13 +394,13 @@ def test_is_static_gain(self):
         C1 = np.eye(2)
         D0 = 0
         D1 = np.ones((2,1))
-        assert StateSpace(A0, B0, C1, D1).is_static_gain()
-        assert not StateSpace(A1, B0, C1, D1).is_static_gain()
-        assert not StateSpace(A0, B1, C1, D1).is_static_gain()
-        assert not StateSpace(A1, B1, C1, D1).is_static_gain()
-        assert StateSpace(A0, B0, C0, D0).is_static_gain()
-        assert StateSpace(A0, B0, C0, D1).is_static_gain()
-        assert StateSpace(A0, B0, C1, D0).is_static_gain()
+        assert StateSpace(A0, B0, C1, D1)._isstatic()
+        assert not StateSpace(A1, B0, C1, D1)._isstatic()
+        assert not StateSpace(A0, B1, C1, D1)._isstatic()
+        assert not StateSpace(A1, B1, C1, D1)._isstatic()
+        assert StateSpace(A0, B0, C0, D0)._isstatic()
+        assert StateSpace(A0, B0, C0, D1)._isstatic()
+        assert StateSpace(A0, B0, C1, D0)._isstatic()
 
     @slycotonly
     def test_minreal(self):
diff --git a/control/tests/xferfcn_test.py b/control/tests/xferfcn_test.py
index 73498ea44..782fcaa13 100644
--- a/control/tests/xferfcn_test.py
+++ b/control/tests/xferfcn_test.py
@@ -406,7 +406,7 @@ def test_slice(self):
         assert (sys1.ninputs, sys1.noutputs) == (2, 1)
         assert sys1.dt == 0.5
 
-    def test_is_static_gain(self):
+    def test__isstatic(self):
         numstatic = 1.1
         denstatic = 1.2
         numdynamic = [1, 1]
@@ -415,18 +415,18 @@ def test_is_static_gain(self):
         denstaticmimo = [[[1.9,], [1.2,]], [[1.2,], [0.8,]]]
         numdynamicmimo = [[[1.1, 0.9], [1.2]], [[1.2], [0.8]]]
         dendynamicmimo = [[[1.1, 0.7], [0.2]], [[1.2], [0.8]]]
-        assert TransferFunction(numstatic, denstatic).is_static_gain()
-        assert TransferFunction(numstaticmimo, denstaticmimo).is_static_gain()
+        assert TransferFunction(numstatic, denstatic)._isstatic()
+        assert TransferFunction(numstaticmimo, denstaticmimo)._isstatic()
 
-        assert not TransferFunction(numstatic, dendynamic).is_static_gain()
-        assert not TransferFunction(numdynamic, dendynamic).is_static_gain()
-        assert not TransferFunction(numdynamic, denstatic).is_static_gain()
-        assert not TransferFunction(numstatic, dendynamic).is_static_gain()
+        assert not TransferFunction(numstatic, dendynamic)._isstatic()
+        assert not TransferFunction(numdynamic, dendynamic)._isstatic()
+        assert not TransferFunction(numdynamic, denstatic)._isstatic()
+        assert not TransferFunction(numstatic, dendynamic)._isstatic()
 
         assert not TransferFunction(numstaticmimo,
-                                    dendynamicmimo).is_static_gain()
+                                    dendynamicmimo)._isstatic()
         assert not TransferFunction(numdynamicmimo,
-                                    denstaticmimo).is_static_gain()
+                                    denstaticmimo)._isstatic()
 
     @pytest.mark.parametrize("omega, resp",
                              [(1, np.array([[-0.5 - 0.5j]])),
diff --git a/control/timeresp.py b/control/timeresp.py
index 405a4b582..55ced8302 100644
--- a/control/timeresp.py
+++ b/control/timeresp.py
@@ -1122,7 +1122,7 @@ def _ideal_tfinal_and_dt(sys, is_step=True):
     pts_per_cycle = 25  # Number of points divide a period of oscillation
     log_decay_percent = np.log(100)  # Factor of reduction for real pole decays
 
-    if sys.is_static_gain():
+    if sys._isstatic():
         tfinal = default_tfinal
         dt = sys.dt if isdtime(sys, strict=True) else default_dt
     elif isdtime(sys, strict=True):
diff --git a/control/xferfcn.py b/control/xferfcn.py
index 5efee302f..157ac6212 100644
--- a/control/xferfcn.py
+++ b/control/xferfcn.py
@@ -214,7 +214,7 @@ def __init__(self, *args, **kwargs):
             # no dt given in positional arguments
             if 'dt' in kwargs:
                 dt = kwargs['dt']
-            elif self.is_static_gain():
+            elif self._isstatic():
                 dt = None
             else:
                 dt = config.defaults['control.default_dt']
@@ -228,7 +228,7 @@ def __init__(self, *args, **kwargs):
             try:
                 dt = args[0].dt
             except AttributeError:
-                if self.is_static_gain():
+                if self._isstatic():
                     dt = None
                 else:
                     dt = config.defaults['control.default_dt']
@@ -1084,7 +1084,7 @@ def _dcgain_cont(self):
                         gain[i][j] = np.nan
         return np.squeeze(gain)
 
-    def is_static_gain(self):
+    def _isstatic(self):
          """returns True if and only if all of the numerator and denominator
          polynomials of the (possibly MIMO) transfer function are zeroth order,
          that is, if the system has no dynamics. """