diff --git a/include/cantera/equil/MultiPhase.h b/include/cantera/equil/MultiPhase.h
index 0971fe117..6b8bf2ebd 100644
--- a/include/cantera/equil/MultiPhase.h
+++ b/include/cantera/equil/MultiPhase.h
@@ -65,7 +65,7 @@ public:
 
     //! Destructor. Does nothing. Class MultiPhase does not take "ownership"
     //! (that is, responsibility for destroying) the phase objects.
-    virtual ~MultiPhase() = default;
+    virtual ~MultiPhase();
 
     //! Add a vector of phases to the mixture
     /*!
diff --git a/src/equil/MultiPhase.cpp b/src/equil/MultiPhase.cpp
index a5b967904..fd6c7a0a3 100644
--- a/src/equil/MultiPhase.cpp
+++ b/src/equil/MultiPhase.cpp
@@ -20,6 +20,13 @@ using namespace std;
 namespace Cantera
 {
 
+MultiPhase::~MultiPhase()
+{
+    for (size_t i = 0; i < m_phase.size(); i++) {
+        m_phase[i]->removeSpeciesLock();
+    }
+}
+
 void MultiPhase::addPhases(MultiPhase& mix)
 {
     for (size_t n = 0; n < mix.nPhases(); n++) {
@@ -101,6 +108,9 @@ void MultiPhase::addPhase(ThermoPhase* p, double moles)
         m_Tmin = std::max(p->minTemp(), m_Tmin);
         m_Tmax = std::min(p->maxTemp(), m_Tmax);
     }
+
+    // lock species list
+    p->addSpeciesLock();
 }
 
 void MultiPhase::init()