diff --git a/include/cantera/thermo/Phase.h b/include/cantera/thermo/Phase.h
index fedf5c812..caec1b758 100644
--- a/include/cantera/thermo/Phase.h
+++ b/include/cantera/thermo/Phase.h
@@ -761,7 +761,7 @@ public:
     //! Add a Species to this Phase. Returns `true` if the species was
     //! successfully added, or `false` if the species was ignored.
     //! @see ignoreUndefinedElements addUndefinedElements throwUndefinedElements
-    virtual bool addSpecies(shared_ptr<Species>& spec);
+    virtual bool addSpecies(shared_ptr<Species> spec);
 
     void addSpecies(const std::string& name, const doublereal* comp,
                     doublereal charge = 0.0, doublereal size = 1.0);
diff --git a/include/cantera/thermo/ThermoPhase.h b/include/cantera/thermo/ThermoPhase.h
index cb538b115..8d9e71feb 100644
--- a/include/cantera/thermo/ThermoPhase.h
+++ b/include/cantera/thermo/ThermoPhase.h
@@ -1310,7 +1310,7 @@ public:
     //@{
 
     using Phase::addSpecies;
-    virtual bool addSpecies(shared_ptr<Species>& spec);
+    virtual bool addSpecies(shared_ptr<Species> spec);
 
     //! Store a reference pointer to the XML tree containing the species data
     //! for this phase.
diff --git a/src/thermo/Phase.cpp b/src/thermo/Phase.cpp
index 561394908..2c59ebbe4 100644
--- a/src/thermo/Phase.cpp
+++ b/src/thermo/Phase.cpp
@@ -837,7 +837,7 @@ size_t Phase::addUniqueElementAfterFreeze(const std::string& symbol,
     return addElement(symbol, weight, atomicNumber, entropy298, elem_type);
 }
 
-bool Phase::addSpecies(shared_ptr<Species>& spec) {
+bool Phase::addSpecies(shared_ptr<Species> spec) {
     m_species[spec->name] = spec;
     vector_fp comp(nElements());
     for (map<string, double>::const_iterator iter = spec->composition.begin();
diff --git a/src/thermo/ThermoPhase.cpp b/src/thermo/ThermoPhase.cpp
index 2fd4911e6..ce76ae726 100644
--- a/src/thermo/ThermoPhase.cpp
+++ b/src/thermo/ThermoPhase.cpp
@@ -694,7 +694,7 @@ void ThermoPhase::installSlavePhases(Cantera::XML_Node* phaseNode)
 {
 }
 
-bool ThermoPhase::addSpecies(shared_ptr<Species>& spec)
+bool ThermoPhase::addSpecies(shared_ptr<Species> spec)
 {
     bool added = Phase::addSpecies(spec);
     if (added) {