diff --git a/include/cantera/thermo/IdealSolidSolnPhase.h b/include/cantera/thermo/IdealSolidSolnPhase.h
index 98e737064..05316b5c0 100644
--- a/include/cantera/thermo/IdealSolidSolnPhase.h
+++ b/include/cantera/thermo/IdealSolidSolnPhase.h
@@ -578,6 +578,22 @@ public:
     virtual void initThermoXML(XML_Node& phaseNode, const std::string& id);
     virtual void setToEquilState(const doublereal* lambda_RT);
 
+    //! Set the form for the standard and generalized concentrations
+    /*!
+     * Must be one of 'unity', 'molar_volume', or 'solvent_volume'.
+     * The default is 'unity'.
+     *
+     *  | m_formGC       | GeneralizedConc | StandardConc |
+     *  | -----------    | --------------- | ------------ |
+     *  | unity          | X_k             | 1.0          |
+     *  | molar_volume   | X_k / V_k       | 1.0 / V_k    |
+     *  | solvent_volume | X_k / V_N       | 1.0 / V_N    |
+     *
+     *  The value and form of the generalized concentration will affect
+     *  reaction rate constants involving species in this phase.
+     */
+    void setStandardConcentrationModel(const std::string& model);
+
     /**
      * Report the molar volume of species k
      *
@@ -603,16 +619,9 @@ protected:
     virtual void compositionChanged();
 
     /**
-     *  Format for the generalized concentrations.
-     *
-     *  | m_formGC    | GeneralizedConc | StandardConc |
-     *  | ----------- | --------------- | ------------ |
-     *  | 0 (default) | X_k             | 1.0          |
-     *  | 1           | X_k / V_k       | 1.0 / V_k    |
-     *  | 2           | X_k / V_N       | 1.0 / V_N    |
-     *
-     *  The value and form of the generalized concentration will affect
-     *  reaction rate constants involving species in this phase.
+     * The standard concentrations can have one of three different forms:
+     * 0 = 'unity', 1 = 'molar_volume', 2 = 'solvent_volume'. See
+     * setStandardConcentrationModel().
      */
     int m_formGC;
 
diff --git a/src/thermo/IdealSolidSolnPhase.cpp b/src/thermo/IdealSolidSolnPhase.cpp
index 5c1fda1bb..df5000566 100644
--- a/src/thermo/IdealSolidSolnPhase.cpp
+++ b/src/thermo/IdealSolidSolnPhase.cpp
@@ -359,7 +359,12 @@ bool IdealSolidSolnPhase::addSpecies(shared_ptr<Species> spec)
         m_s0_R.push_back(0.0);
         m_pe.push_back(0.0);;
         m_pp.push_back(0.0);
-        m_speciesMolarVolume.push_back(0.0);
+        if (spec->extra.hasKey("molar_volume")) {
+            m_speciesMolarVolume.push_back(spec->extra["molar_volume"].asDouble());
+        } else {
+            throw CanteraError("IdealSolidSolnPhase::addSpecies",
+                "Molar volume not specified for species '{}'", spec->name);
+        }
     }
     return added;
 }
@@ -391,34 +396,12 @@ void IdealSolidSolnPhase::initThermoXML(XML_Node& phaseNode, const std::string&
     //     <standardConc model="molar_volume" />
     //     <standardConc model="solvent_volume" />
     if (phaseNode.hasChild("standardConc")) {
-        XML_Node& scNode = phaseNode.child("standardConc");
-        string formString = scNode.attrib("model");
-        if (ba::iequals(formString, "unity")) {
-            m_formGC = 0;
-        } else if (ba::iequals(formString, "molar_volume")) {
-            m_formGC = 1;
-        } else if (ba::iequals(formString, "solvent_volume")) {
-            m_formGC = 2;
-        } else {
-            throw CanteraError("IdealSolidSolnPhase::initThermoXML",
-                               "Unknown standardConc model: " + formString);
-        }
+        setStandardConcentrationModel(phaseNode.child("standardConc")["model"]);
     } else {
         throw CanteraError("IdealSolidSolnPhase::initThermoXML",
                            "Unspecified standardConc model");
     }
 
-    // Now go get the molar volumes
-    XML_Node& speciesList = phaseNode.child("speciesArray");
-    XML_Node* speciesDB = get_XML_NameID("speciesData", speciesList["datasrc"],
-                                         &phaseNode.root());
-
-    for (size_t k = 0; k < m_kk; k++) {
-        XML_Node* s = speciesDB->findByAttr("name", speciesName(k));
-        XML_Node* ss = s->findByName("standardState");
-        m_speciesMolarVolume[k] = getFloat(*ss, "molarVolume", "toSI");
-    }
-
     // Call the base initThermo, which handles setting the initial state.
     ThermoPhase::initThermoXML(phaseNode, id_);
 }
@@ -440,6 +423,20 @@ void IdealSolidSolnPhase::setToEquilState(const doublereal* lambda_RT)
     setState_PX(pres, &m_pp[0]);
 }
 
+void IdealSolidSolnPhase::setStandardConcentrationModel(const std::string& model)
+{
+    if (ba::iequals(model, "unity")) {
+        m_formGC = 0;
+    } else if (ba::iequals(model, "molar_volume")) {
+        m_formGC = 1;
+    } else if (ba::iequals(model, "solvent_volume")) {
+        m_formGC = 2;
+    } else {
+        throw CanteraError("IdealSolidSolnPhase::setStandardConcentrationModel",
+                           "Unknown standard concentration model '{}'", model);
+    }
+}
+
 double IdealSolidSolnPhase::speciesMolarVolume(int k) const
 {
     return m_speciesMolarVolume[k];
diff --git a/test/thermo/phaseConstructors.cpp b/test/thermo/phaseConstructors.cpp
index 6066110b8..3e935df2c 100644
--- a/test/thermo/phaseConstructors.cpp
+++ b/test/thermo/phaseConstructors.cpp
@@ -15,6 +15,8 @@
 #include "cantera/thermo/LatticePhase.h"
 #include "cantera/thermo/StoichSubstance.h"
 #include "cantera/thermo/LatticeSolidPhase.h"
+#include "cantera/thermo/IdealSolidSolnPhase.h"
+
 #include "cantera/thermo/NasaPoly2.h"
 #include "cantera/thermo/ConstCpPoly.h"
 #include "cantera/thermo/ShomatePoly.h"
@@ -479,4 +481,24 @@ TEST(LatticeSolidPhase, fromScratch)
     }
 }
 
+TEST(IdealSolidSolnPhase, fromScratch)
+{
+    // Regression test based fictitious XML input file
+    IdealSolidSolnPhase p;
+    p.addUndefinedElements();
+    auto sp1 = make_species("sp1", "C:2, H:2", o2_nasa_coeffs);
+    sp1->extra["molar_volume"] = 1.5;
+    auto sp2 = make_species("sp2", "C:1", h2o_nasa_coeffs);
+    sp2->extra["molar_volume"] = 1.3;
+    auto sp3 = make_species("sp3", "H:2", h2_nasa_coeffs);
+    sp3->extra["molar_volume"] = 0.1;
+    for (auto& s : {sp1, sp2, sp3}) {
+        p.addSpecies(s);
+    }
+    p.setState_TPX(500, 2e5, "sp1:0.1, sp2:0.89, sp3:0.01");
+    EXPECT_NEAR(p.density(), 10.1786978, 1e-6);
+    EXPECT_NEAR(p.enthalpy_mass(), -15642803.3884617, 1e-4);
+    EXPECT_NEAR(p.gibbs_mole(), -313642293.1654253, 1e-4);
+}
+
 } // namespace Cantera