diff --git a/include/cantera/zeroD/ReactorBase.h b/include/cantera/zeroD/ReactorBase.h
index 5f529b42c..856397f9b 100644
--- a/include/cantera/zeroD/ReactorBase.h
+++ b/include/cantera/zeroD/ReactorBase.h
@@ -133,10 +133,18 @@ public:
 
     //! return a reference to the contents.
     thermo_t& contents() {
+        if (!m_thermo) {
+            throw CanteraError("ReactorBase::contents",
+                               "Reactor contents not defined.");
+        }
         return *m_thermo;
     }
 
     const thermo_t& contents() const {
+        if (!m_thermo) {
+            throw CanteraError("ReactorBase::contents",
+                               "Reactor contents not defined.");
+        }
         return *m_thermo;
     }
 
diff --git a/src/zeroD/FlowDevice.cpp b/src/zeroD/FlowDevice.cpp
index 00c3bac63..20286637b 100644
--- a/src/zeroD/FlowDevice.cpp
+++ b/src/zeroD/FlowDevice.cpp
@@ -19,10 +19,6 @@ bool FlowDevice::install(ReactorBase& in, ReactorBase& out)
     // construct adapters between inlet and outlet species
     ThermoPhase* mixin = &m_in->contents();
     ThermoPhase* mixout = &m_out->contents();
-    if (mixin == 0 || mixout == 0) {
-        throw CanteraError("FlowDevice::install", "Can't install flow device "
-            "until reactor contents have been assigned.");
-    }
 
     m_nspin = mixin->nSpecies();
     m_nspout = mixout->nSpecies();