diff --git a/include/cantera/thermo/GeneralSpeciesThermo.h b/include/cantera/thermo/GeneralSpeciesThermo.h
index 44b04daa9..10fe464f2 100644
--- a/include/cantera/thermo/GeneralSpeciesThermo.h
+++ b/include/cantera/thermo/GeneralSpeciesThermo.h
@@ -133,11 +133,14 @@ private:
     const SpeciesThermoInterpType* provideSTIT(size_t k) const;
 
 protected:
-    typedef std::map<int, std::vector<shared_ptr<SpeciesThermoInterpType> > > STIT_map;
+    typedef std::pair<size_t, shared_ptr<SpeciesThermoInterpType> > index_STIT;
+    typedef std::map<int, std::vector<index_STIT> > STIT_map;
     typedef std::map<int, std::vector<double> > tpoly_map;
     /**
-     * This is the main unknown in the object. It contains pointers to
+     * This is the main data structure, which contains the
      * SpeciesThermoInterpType objects, sorted by the parameterization type.
+     * `m_sp[i]` is the vector of [species index, STIT] pairs which use
+     * parameterization `i`.
      */
     STIT_map m_sp;
 
diff --git a/src/thermo/GeneralSpeciesThermo.cpp b/src/thermo/GeneralSpeciesThermo.cpp
index c0ac3236b..3a5f3df5d 100644
--- a/src/thermo/GeneralSpeciesThermo.cpp
+++ b/src/thermo/GeneralSpeciesThermo.cpp
@@ -32,8 +32,10 @@ GeneralSpeciesThermo::GeneralSpeciesThermo(const GeneralSpeciesThermo& b) :
          iter != b.m_sp.end();
          iter++) {
         for (size_t k = 0; k < iter->second.size(); k++) {
-            shared_ptr<SpeciesThermoInterpType> spec(iter->second[k]->duplMyselfAsSpeciesThermoInterpType());
-            m_sp[iter->first].push_back(spec);
+            size_t i = iter->second[k].first;
+            shared_ptr<SpeciesThermoInterpType> spec(
+                iter->second[k].second->duplMyselfAsSpeciesThermoInterpType());
+            m_sp[iter->first].push_back(std::make_pair(i, spec));
         }
     }
 }
@@ -52,8 +54,10 @@ GeneralSpeciesThermo::operator=(const GeneralSpeciesThermo& b)
          iter != b.m_sp.end();
          iter++) {
         for (size_t k = 0; k < iter->second.size(); k++) {
-            shared_ptr<SpeciesThermoInterpType> spec(iter->second[k]->duplMyselfAsSpeciesThermoInterpType());
-            m_sp[iter->first].push_back(spec);
+            size_t i = iter->second[k].first;
+            shared_ptr<SpeciesThermoInterpType> spec(
+                iter->second[k].second->duplMyselfAsSpeciesThermoInterpType());
+            m_sp[iter->first].push_back(std::make_pair(i, spec));
         }
     }
 
@@ -106,10 +110,9 @@ void GeneralSpeciesThermo::install_STIT(size_t index,
     }
     AssertThrow(m_speciesLoc.find(index) == m_speciesLoc.end(),
                 "Index position isn't null, duplication of assignment: " + int2str(index));
-    stit_ptr->setIndex(index);
     int type = stit_ptr->reportType();
     m_speciesLoc[index] = std::make_pair(type, m_sp[type].size());
-    m_sp[type].push_back(stit_ptr);
+    m_sp[type].push_back(std::make_pair(index, stit_ptr));
     if (m_sp[type].size() == 1) {
         m_tpoly[type].resize(stit_ptr->temperaturePolySize());
     }
@@ -132,7 +135,7 @@ void GeneralSpeciesThermo::update_one(size_t k, doublereal t, doublereal* cp_R,
 {
     const SpeciesThermoInterpType* sp_ptr = provideSTIT(k);
     if (sp_ptr) {
-        sp_ptr->updatePropertiesTemp(t, cp_R, h_RT, s_R);
+        sp_ptr->updatePropertiesTemp(t, cp_R+k, h_RT+k, s_R+k);
     }
 }
 
@@ -142,11 +145,12 @@ void GeneralSpeciesThermo::update(doublereal t, doublereal* cp_R,
     STIT_map::const_iterator iter = m_sp.begin();
     tpoly_map::iterator jter = m_tpoly.begin();
     for (; iter != m_sp.end(); iter++, jter++) {
-        const std::vector<shared_ptr<SpeciesThermoInterpType> >& species = iter->second;
+        const std::vector<index_STIT>& species = iter->second;
         double* tpoly = &jter->second[0];
-        species[0]->updateTemperaturePoly(t, tpoly);
+        species[0].second->updateTemperaturePoly(t, tpoly);
         for (size_t k = 0; k < species.size(); k++) {
-            species[k]->updateProperties(tpoly, cp_R, h_RT, s_R);
+            size_t i = species[k].first;
+            species[k].second->updateProperties(tpoly, cp_R+i, h_RT+i, s_R+i);
         }
     }
 }
@@ -215,7 +219,7 @@ SpeciesThermoInterpType* GeneralSpeciesThermo::provideSTIT(size_t k)
 {
     try {
         const std::pair<int, size_t>& loc = getValue(m_speciesLoc, k);
-        return getValue(m_sp, loc.first)[loc.second].get();
+        return getValue(m_sp, loc.first)[loc.second].second.get();
     } catch (std::out_of_range&) {
         return 0;
     }
@@ -225,7 +229,7 @@ const SpeciesThermoInterpType* GeneralSpeciesThermo::provideSTIT(size_t k) const
 {
     try {
         const std::pair<int, size_t>& loc = getValue(m_speciesLoc, k);
-        return getValue(m_sp, loc.first)[loc.second].get();
+        return getValue(m_sp, loc.first)[loc.second].second.get();
     } catch (std::out_of_range&) {
         return 0;
     }