diff --git a/include/cantera/thermo/MolarityIonicVPSSTP.h b/include/cantera/thermo/MolarityIonicVPSSTP.h
index b05235b37..e45e3a030 100644
--- a/include/cantera/thermo/MolarityIonicVPSSTP.h
+++ b/include/cantera/thermo/MolarityIonicVPSSTP.h
@@ -237,9 +237,6 @@ protected:
     //! Number of pseudo binary species
     size_t numPBSpecies_;
 
-    //! index of special species
-    size_t indexSpecialSpecies_;
-
     mutable vector_fp PBMoleFractions_;
 
     //! Vector of cation indices in the mixture
diff --git a/src/thermo/MolarityIonicVPSSTP.cpp b/src/thermo/MolarityIonicVPSSTP.cpp
index 68ba612e8..f6dcdbd3a 100644
--- a/src/thermo/MolarityIonicVPSSTP.cpp
+++ b/src/thermo/MolarityIonicVPSSTP.cpp
@@ -28,7 +28,6 @@ namespace Cantera
 MolarityIonicVPSSTP::MolarityIonicVPSSTP() :
     PBType_(PBTYPE_PASSTHROUGH),
     numPBSpecies_(m_kk),
-    indexSpecialSpecies_(npos),
     neutralPBindexStart(0)
 {
 }
@@ -37,7 +36,6 @@ MolarityIonicVPSSTP::MolarityIonicVPSSTP(const std::string& inputFile,
         const std::string& id_) :
     PBType_(PBTYPE_PASSTHROUGH),
     numPBSpecies_(m_kk),
-    indexSpecialSpecies_(npos),
     neutralPBindexStart(0)
 {
     initThermoFile(inputFile, id_);
@@ -47,7 +45,6 @@ MolarityIonicVPSSTP::MolarityIonicVPSSTP(XML_Node& phaseRoot,
         const std::string& id_) :
     PBType_(PBTYPE_PASSTHROUGH),
     numPBSpecies_(m_kk),
-    indexSpecialSpecies_(npos),
     neutralPBindexStart(0)
 {
     importPhase(phaseRoot, this);