diff --git a/include/cantera/zeroD/flowControllers.h b/include/cantera/zeroD/flowControllers.h
index 73b8807cd5..c301043f3c 100644
--- a/include/cantera/zeroD/flowControllers.h
+++ b/include/cantera/zeroD/flowControllers.h
@@ -54,7 +54,7 @@ class PressureController : public FlowDevice
     }
 
     virtual bool ready() {
-        return FlowDevice::ready() && m_master != 0;
+        return FlowDevice::ready() && m_master != 0 && m_coeffs.size() == 1;
     }
 
     void setMaster(FlowDevice* master) {
@@ -62,6 +62,10 @@ class PressureController : public FlowDevice
     }
 
     virtual void updateMassFlowRate(doublereal time) {
+        if (!ready()) {
+            throw CanteraError("PressureController::updateMassFlowRate",
+                "Device is not ready; some parameters have not been set.");
+        }
         doublereal master_mdot = m_master->massFlowRate(time);
         m_mdot = master_mdot + m_coeffs[0]*(in().pressure() -
                                             out().pressure());
@@ -72,7 +76,8 @@ class PressureController : public FlowDevice
     FlowDevice* m_master;
 };
 
-//! Supply a mass flow rate that is a function of the pressure drop across the valve. 
+//! Supply a mass flow rate that is a function of the pressure drop across the
+//! valve.
 /*!
  * The default behavior is a linearly proportional to the pressure difference.
  * Note that real valves do not have this behavior, so this class does not
@@ -86,11 +91,15 @@ class Valve : public FlowDevice
     }
 
     virtual bool ready() {
-        return FlowDevice::ready() && m_coeffs.size() >= 1;
+        return FlowDevice::ready() && (m_coeffs.size() == 1 || m_func);
     }
 
     /// Compute the currrent mass flow rate, based on the pressure difference.
     virtual void updateMassFlowRate(doublereal time) {
+        if (!ready()) {
+            throw CanteraError("Valve::updateMassFlowRate",
+                "Device is not ready; some parameters have not been set.");
+        }
         double delta_P = in().pressure() - out().pressure();
         if (m_func) {
             m_mdot = m_func->eval(delta_P);
diff --git a/interfaces/cython/cantera/_cantera.pxd b/interfaces/cython/cantera/_cantera.pxd
index d50389605b..91ecd9c483 100644
--- a/interfaces/cython/cantera/_cantera.pxd
+++ b/interfaces/cython/cantera/_cantera.pxd
@@ -517,7 +517,7 @@ cdef extern from "cantera/zeroD/Wall.h":
 cdef extern from "cantera/zeroD/flowControllers.h":
     cdef cppclass CxxFlowDevice "Cantera::FlowDevice":
         CxxFlowDevice()
-        double massFlowRate(double)
+        double massFlowRate(double) except +
         cbool install(CxxReactorBase&, CxxReactorBase&)
         void setFunction(CxxFunc1*)
         void setParameters(int, double*)
diff --git a/interfaces/cython/cantera/test/test_reactor.py b/interfaces/cython/cantera/test/test_reactor.py
index ae8d810790..9417816965 100644
--- a/interfaces/cython/cantera/test/test_reactor.py
+++ b/interfaces/cython/cantera/test/test_reactor.py
@@ -457,6 +457,25 @@ def test_pressure_controller(self):
             dP = self.r1.thermo.P - outlet_reservoir.thermo.P
             self.assertNear(mdot(t) + 1e-5 * dP, pc.mdot(t))
 
+    def test_pressure_controller_errors(self):
+        self.make_reactors()
+        res = ct.Reservoir(self.gas1)
+        mfc = ct.MassFlowController(res, self.r1, mdot=0.6)
+
+        p = ct.PressureController(self.r1, self.r2, master=mfc, K=0.5)
+
+        with self.assertRaises(RuntimeError):
+            p = ct.PressureController(self.r1, self.r2, K=0.5)
+            p.mdot(0.0)
+
+        with self.assertRaises(RuntimeError):
+            p = ct.PressureController(self.r1, self.r2, master=mfc)
+            p.mdot(0.0)
+
+        with self.assertRaises(RuntimeError):
+            p = ct.PressureController(self.r1, self.r2)
+            p.mdot(0.0)
+
     def test_set_initial_time(self):
         self.make_reactors(P1=10*ct.one_atm, X1='AR:1.0', X2='O2:1.0')
         self.net.rtol = 1e-12