diff --git a/Cantera/src/PureFluidPhase.cpp b/Cantera/src/PureFluidPhase.cpp
index b020e0d6c..d2faa918a 100644
--- a/Cantera/src/PureFluidPhase.cpp
+++ b/Cantera/src/PureFluidPhase.cpp
@@ -142,11 +142,11 @@ namespace Cantera {
     }
 
 
-    doublereal PureFluidPhase::isothermalCompressibility() {
+    doublereal PureFluidPhase::isothermalCompressibility() const {
         return m_sub->isothermalCompressibility();
     }
 
-    doublereal PureFluidPhase::thermalExpansionCoeff() {
+    doublereal PureFluidPhase::thermalExpansionCoeff() const {
         return m_sub->thermalExpansionCoeff();
     }
 
diff --git a/Cantera/src/PureFluidPhase.h b/Cantera/src/PureFluidPhase.h
index ee560a052..e10efbfb1 100644
--- a/Cantera/src/PureFluidPhase.h
+++ b/Cantera/src/PureFluidPhase.h
@@ -53,8 +53,8 @@ namespace Cantera {
             mu[0] = gibbs_mole();
         }
 
-        virtual doublereal isothermalCompressibility();
-        virtual doublereal thermalExpansionCoeff();
+        virtual doublereal isothermalCompressibility() const;
+        virtual doublereal thermalExpansionCoeff() const;
 
         tpx::Substance& TPX_Substance();