diff --git a/include/cantera/thermo/DebyeHuckel.h b/include/cantera/thermo/DebyeHuckel.h
index f7cd57c5e..7b7936de6 100644
--- a/include/cantera/thermo/DebyeHuckel.h
+++ b/include/cantera/thermo/DebyeHuckel.h
@@ -937,7 +937,7 @@ private:
      *
      * @param IionicMolality Value of the ionic molality (sqrt(gmol/kg))
      */
-    double _nonpolarActCoeff(double IionicMolality) const;
+    static double _nonpolarActCoeff(double IionicMolality);
 
     //! Formula for the osmotic coefficient that occurs in the GWB.
     /*!
diff --git a/src/thermo/DebyeHuckel.cpp b/src/thermo/DebyeHuckel.cpp
index 935ec46a0..c612b8e0f 100644
--- a/src/thermo/DebyeHuckel.cpp
+++ b/src/thermo/DebyeHuckel.cpp
@@ -936,7 +936,7 @@ bool DebyeHuckel::addSpecies(shared_ptr<Species> spec)
     return added;
 }
 
-double DebyeHuckel::_nonpolarActCoeff(double IionicMolality) const
+double DebyeHuckel::_nonpolarActCoeff(double IionicMolality)
 {
      // These are coefficients to describe the increase in activity coeff for
      // non-polar molecules due to the electrolyte becoming stronger (the so-