diff --git a/Cantera/src/thermo/HKFT_PDSS.cpp b/Cantera/src/thermo/HKFT_PDSS.cpp
index 2b1565ffd..db4d2d624 100644
--- a/Cantera/src/thermo/HKFT_PDSS.cpp
+++ b/Cantera/src/thermo/HKFT_PDSS.cpp
@@ -17,6 +17,8 @@ namespace Cantera {
 
 
 
+
+
   HKFT_PDSS::HKFT_PDSS(ThermoPhase *tp, int spindex) :
     PDSS(tp, spindex)
   {
@@ -342,6 +344,13 @@ namespace Cantera {
     throw CanteraError("HKFT_PDSS::satPressure()", "unimplemented");
     return (0.0);
   }
-    
+   
+  //! Internal formula for the calculation of a_g()
+  double HKFT_PDSS::ag(const double temp) const {
+    static double ag_coeff[3] = { -2.037662,  5.747000E-3,  -6.557892E-6};
+    double t2 = temp * temp;
+    double val = ag_coeff[0] + ag_coeff[1] * temp * ag_coeff[2] * t2;
+    return val;
+  }
 
 }
diff --git a/Cantera/src/thermo/HKFT_PDSS.h b/Cantera/src/thermo/HKFT_PDSS.h
index 74220339b..b326bd98c 100644
--- a/Cantera/src/thermo/HKFT_PDSS.h
+++ b/Cantera/src/thermo/HKFT_PDSS.h
@@ -134,6 +134,9 @@ namespace Cantera {
     virtual void initThermo();
     virtual void setParametersFromXML(const XML_Node& eosdata);
 
+  private:
+    double ag(const double temp) const;
+
   protected:
 
 
diff --git a/Cantera/src/thermo/Makefile.in b/Cantera/src/thermo/Makefile.in
index 8f4b09f3b..70e0d71ce 100644
--- a/Cantera/src/thermo/Makefile.in
+++ b/Cantera/src/thermo/Makefile.in
@@ -58,13 +58,13 @@ ELECTRO_OBJ = MolalityVPSSTP.o  VPStandardStateTP.o \
               WaterPropsIAPWSphi.o WaterPropsIAPWS.o WaterProps.o \
               PDSS.o WaterPDSS.o \
 	      HMWSoln.o HMWSoln_input.o DebyeHuckel.o \
-              IdealGasPDSS.o WaterSSTP.o
+              IdealGasPDSS.o WaterSSTP.o HKFT_PDSS.o
 
 ELECTRO_H = MolalityVPSSTP.h  VPStandardStateTP.h \
                IdealMolalSoln.h \
                WaterPropsIAPWSphi.h WaterPropsIAPWS.h WaterProps.h \
                PDSS.h WaterPDSS.h HMWSoln.h electrolytes.h \
-	       DebyeHuckel.h IdealGasPDSS.h WaterSSTP.h
+	       DebyeHuckel.h IdealGasPDSS.h WaterSSTP.h HKFT_PDSS.h
 endif
 ifeq ($(do_issp),1)
 ISSP_OBJ = IdealSolidSolnPhase.o  StoichSubstanceSSTP.o SingleSpeciesTP.o