diff --git a/include/cantera/thermo/RedlichKisterVPSSTP.h b/include/cantera/thermo/RedlichKisterVPSSTP.h
index 24bda80e6..694bb9bc4 100644
--- a/include/cantera/thermo/RedlichKisterVPSSTP.h
+++ b/include/cantera/thermo/RedlichKisterVPSSTP.h
@@ -442,6 +442,7 @@ public:
      *      nonideal term
      *  @param voltsOut Output contribution to the voltage corresponding to
      *      nonideal term and mf term
+     *  @deprecated Probably broken. To be removed after Cantera 2.3.
      */
     void Vint(double& VintOut, double& voltsOut);
 
diff --git a/src/thermo/RedlichKisterVPSSTP.cpp b/src/thermo/RedlichKisterVPSSTP.cpp
index 36da84c97..fcf22ad6b 100644
--- a/src/thermo/RedlichKisterVPSSTP.cpp
+++ b/src/thermo/RedlichKisterVPSSTP.cpp
@@ -614,6 +614,8 @@ void RedlichKisterVPSSTP::readXMLBinarySpecies(XML_Node& xmLBinarySpecies)
 
 void RedlichKisterVPSSTP::Vint(double& VintOut, double& voltsOut)
 {
+    warn_deprecated("RedlichKisterVPSSTP::Vint",
+                    "To be removed after Cantera 2.3.");
     double XA;
     doublereal T = temperature();
     double Volts = 0.0;