diff --git a/interfaces/cython/cantera/composite.py b/interfaces/cython/cantera/composite.py
index 29ae219eca..0fed004f57 100644
--- a/interfaces/cython/cantera/composite.py
+++ b/interfaces/cython/cantera/composite.py
@@ -513,9 +513,15 @@ def __init__(self, phase, shape=(0,), states=None, extra=None):
             self._indices = list(np.ndindex(self._shape))
             self._output_dummy = self._states[..., 0]
 
+        reserved = self.__dir__()
+
         self._extra = {}
         if isinstance(extra, dict):
             for name, v in extra.items():
+                if name in reserved:
+                    raise ValueError(
+                        "Unable to create extra column '{}': name is already "
+                        "used by SolutionArray objects.".format(name))
                 if not np.shape(v):
                     self._extra[name] = [v]*self._shape[0]
                 elif len(v) == self._shape[0]:
@@ -526,6 +532,10 @@ def __init__(self, phase, shape=(0,), states=None, extra=None):
 
         elif extra and self._shape == (0,):
             for name in extra:
+                if name in reserved:
+                    raise ValueError(
+                        "Unable to create extra column '{}': name is already "
+                        "used by SolutionArray objects.".format(name))
                 self._extra[name] = []
 
         elif extra:
diff --git a/interfaces/cython/cantera/examples/reactors/ic_engine.py b/interfaces/cython/cantera/examples/reactors/ic_engine.py
index 4dbf527be3..8da6a3c565 100644
--- a/interfaces/cython/cantera/examples/reactors/ic_engine.py
+++ b/interfaces/cython/cantera/examples/reactors/ic_engine.py
@@ -155,7 +155,7 @@ def piston_speed(t):
 # set up output data arrays
 states = ct.SolutionArray(
     cyl.thermo,
-    extra=('t', 'ca', 'V', 'm', 'mdot_in', 'mdot_out', 'dWv_dt', 'heat_release_rate'),
+    extra=('t', 'ca', 'V', 'm', 'mdot_in', 'mdot_out', 'dWv_dt'),
 )
 
 # simulate with a maximum resolution of 1 deg crank angle
@@ -169,8 +169,6 @@ def piston_speed(t):
     # calculate results to be stored
     dWv_dt = - (cyl.thermo.P - ambient_air.thermo.P) * A_piston * \
         piston_speed(sim.time)
-    heat_release_rate = - cyl.volume * ct.gas_constant * cyl.T * \
-        np.sum(gas.standard_enthalpies_RT * cyl.thermo.net_production_rates, 0)
 
     # append output data
     states.append(cyl.thermo.state,
@@ -178,8 +176,7 @@ def piston_speed(t):
                   V=cyl.volume, m=cyl.mass,
                   mdot_in=inlet_valve.mdot(sim.time),
                   mdot_out=outlet_valve.mdot(sim.time),
-                  dWv_dt=dWv_dt,
-                  heat_release_rate=heat_release_rate)
+                  dWv_dt=dWv_dt)
 
 
 #######################################################################
@@ -221,7 +218,7 @@ def ca_ticks(t):
 
 # heat of reaction and expansion work
 fig, ax = plt.subplots()
-ax.plot(t, 1.e-3 * states.heat_release_rate, label=r'$\dot{Q}$')
+ax.plot(t, 1.e-3 * states.heat_release_rate * states.V, label=r'$\dot{Q}$')
 ax.plot(t, 1.e-3 * states.dWv_dt, label=r'$\dot{W}_v$')
 ax.set_ylim(-1e2, 1e3)
 ax.legend(loc=0)
@@ -247,7 +244,7 @@ def ca_ticks(t):
 ######################################################################
 
 # heat release
-Q = trapz(states.heat_release_rate, t)
+Q = trapz(states.heat_release_rate * states.V, t)
 print('{:45s}{:>4.1f} kW'.format('Heat release rate per cylinder (estimate):',
                                  Q / t[-1] / 1000.))
 
diff --git a/interfaces/cython/cantera/test/test_thermo.py b/interfaces/cython/cantera/test/test_thermo.py
index b9b8bc7e52..e8bd85f1e8 100644
--- a/interfaces/cython/cantera/test/test_thermo.py
+++ b/interfaces/cython/cantera/test/test_thermo.py
@@ -1641,6 +1641,10 @@ def test_slicing_ndim(self):
         self.assertArrayNear(col3.T, 900*np.ones(2))
         self.assertArrayNear(row2.T, 900*np.ones(5))
 
+    def test_extra(self):
+        with self.assertRaises(ValueError):
+            states = ct.SolutionArray(self.gas, extra=['creation_rates'])
+        
     def test_append(self):
         states = ct.SolutionArray(self.gas, 5)
         states.TPX = np.linspace(500, 1000, 5), 2e5, 'H2:0.5, O2:0.4'