diff --git a/interfaces/cython/cantera/test/test_transport.py b/interfaces/cython/cantera/test/test_transport.py
index 17fb99db2..c033ca3c1 100644
--- a/interfaces/cython/cantera/test/test_transport.py
+++ b/interfaces/cython/cantera/test/test_transport.py
@@ -43,6 +43,51 @@ class TestTransport(utilities.CanteraTest):
         self.assertTrue(all(self.phase.multi_diff_coeffs.flat >= 0.0))
         self.assertTrue(all(self.phase.thermal_diff_coeffs.flat != 0.0))
 
+    def test_add_species_mix(self):
+        S = {s.name: s for s in ct.Species.listFromFile('gri30.xml')}
+
+        base = ['H', 'H2', 'OH', 'O2', 'AR']
+        extra = ['H2O', 'CH4']
+
+        state = 500, 2e5, 'H2:0.4, O2:0.29, CH4:0.01, H2O:0.3'
+
+        gas1 = ct.Solution(thermo='IdealGas', species=[S[s] for s in base+extra])
+        gas1.transport_model = 'Mix'
+        gas1.TPX = state
+
+        gas2 = ct.Solution(thermo='IdealGas', species=[S[s] for s in base])
+        gas2.transport_model = 'Mix'
+        for s in extra:
+            gas2.add_species(S[s])
+        gas2.TPX = state
+
+        self.assertNear(gas1.viscosity, gas2.viscosity)
+        self.assertNear(gas1.thermal_conductivity, gas2.thermal_conductivity)
+        self.assertArrayNear(gas1.binary_diff_coeffs, gas2.binary_diff_coeffs)
+        self.assertArrayNear(gas1.mix_diff_coeffs, gas2.mix_diff_coeffs)
+
+    def test_add_species_multi(self):
+        S = {s.name: s for s in ct.Species.listFromFile('gri30.xml')}
+
+        base = ['H', 'H2', 'OH', 'O2', 'AR', 'N2']
+        extra = ['H2O', 'CH4']
+
+        state = 500, 2e5, 'H2:0.3, O2:0.28, CH4:0.02, H2O:0.3, N2:0.1'
+
+        gas1 = ct.Solution(thermo='IdealGas', species=[S[s] for s in base+extra])
+        gas1.transport_model = 'Multi'
+        gas1.TPX = state
+
+        gas2 = ct.Solution(thermo='IdealGas', species=[S[s] for s in base])
+        gas2.transport_model = 'Multi'
+        for s in extra:
+            gas2.add_species(S[s])
+        gas2.TPX = state
+
+        self.assertNear(gas1.thermal_conductivity, gas2.thermal_conductivity)
+        self.assertArrayNear(gas1.multi_diff_coeffs, gas2.multi_diff_coeffs)
+
+
 class TestTransportGeometryFlags(utilities.CanteraTest):
     phase_data = """
 units(length="cm", time="s", quantity="mol", act_energy="cal/mol")
diff --git a/src/transport/GasTransport.cpp b/src/transport/GasTransport.cpp
index 9b2a42585..5535498a0 100644
--- a/src/transport/GasTransport.cpp
+++ b/src/transport/GasTransport.cpp
@@ -101,6 +101,11 @@ GasTransport& GasTransport::operator=(const GasTransport& right)
 
 void GasTransport::update_T()
 {
+    if (m_thermo->nSpecies() != m_nsp) {
+        // Rebuild data structures if number of species has changed
+        init(m_thermo, m_mode, m_log_level);
+    }
+
     double T = m_thermo->temperature();
     if (T == m_temp) {
         return;
@@ -517,6 +522,10 @@ void GasTransport::fitCollisionIntegrals(MMCollisionInt& integrals)
         }
     }
     vector_fp fitlist;
+    m_omega22_poly.clear();
+    m_astar_poly.clear();
+    m_bstar_poly.clear();
+    m_cstar_poly.clear();
     for (size_t i = 0; i < m_nsp; i++) {
         for (size_t j = i; j < m_nsp; j++) {
             // Chemkin fits only delta* = 0
@@ -557,6 +566,9 @@ void GasTransport::fitProperties(MMCollisionInt& integrals)
     vector_fp tlog(np), spvisc(np), spcond(np);
     vector_fp w(np), w2(np);
 
+    m_visccoeffs.clear();
+    m_condcoeffs.clear();
+
     // generate array of log(t) values
     for (size_t n = 0; n < np; n++) {
         double t = m_thermo->minTemp() + dt*n;
@@ -715,6 +727,7 @@ void GasTransport::fitProperties(MMCollisionInt& integrals)
 
     mxerr = 0.0, mxrelerr = 0.0;
     vector_fp diff(np + 1);
+    m_diffcoeffs.clear();
     for (size_t k = 0; k < m_nsp; k++) {
         for (size_t j = k; j < m_nsp; j++) {
             for (size_t n = 0; n < np; n++) {
diff --git a/src/transport/MixTransport.cpp b/src/transport/MixTransport.cpp
index c57b76433..b84aca997 100644
--- a/src/transport/MixTransport.cpp
+++ b/src/transport/MixTransport.cpp
@@ -123,7 +123,7 @@ void MixTransport::getSpeciesFluxes(size_t ndim, const doublereal* const grad_T,
 void MixTransport::update_T()
 {
     doublereal t = m_thermo->temperature();
-    if (t == m_temp) {
+    if (t == m_temp && m_nsp == m_thermo->nSpecies()) {
         return;
     }
     if (t < 0.0) {
diff --git a/src/transport/MultiTransport.cpp b/src/transport/MultiTransport.cpp
index bbc922342..7be5c765f 100644
--- a/src/transport/MultiTransport.cpp
+++ b/src/transport/MultiTransport.cpp
@@ -388,7 +388,7 @@ void MultiTransport::getMultiDiffCoeffs(const size_t ld, doublereal* const d)
 
 void MultiTransport::update_T()
 {
-    if (m_temp == m_thermo->temperature()) {
+    if (m_temp == m_thermo->temperature() && m_nsp == m_thermo->nSpecies()) {
         return;
     }
     GasTransport::update_T();