diff --git a/interfaces/python/ck2cti.py b/interfaces/python/ck2cti.py
index e26338059..c1e8f5667 100755
--- a/interfaces/python/ck2cti.py
+++ b/interfaces/python/ck2cti.py
@@ -1421,9 +1421,14 @@ class Parser(object):
                         if entryPosition == entryLength-1:
                             label, thermo, comp, note = self.readNasa9Entry(entry)
                             try:
-                                self.speciesDict[label].thermo = thermo
-                                self.speciesDict[label].composition = comp
-                                self.speciesDict[label].note = note
+                                species = self.speciesDict[label]
+                                # use the first set of thermo data found
+                                if species.thermo is not None:
+                                    self.warn('Found additional thermo entry for species {0}'.format(label))
+                                else:
+                                    species.thermo = thermo
+                                    species.composition = comp
+                                    species.note = note
                             except KeyError:
                                 logging.info('Skipping unexpected species "{0}" while reading thermodynamics entry.'.format(label))
 
@@ -1452,9 +1457,14 @@ class Parser(object):
                             if line[79] == '4':
                                 label, thermo, comp, note = self.readThermoEntry(thermo, TintDefault)
                                 try:
-                                    self.speciesDict[label].thermo = thermo
-                                    self.speciesDict[label].composition = comp
-                                    self.speciesDict[label].note = note
+                                    species = self.speciesDict[label]
+                                    # use the first set of thermo data found
+                                    if species.thermo is not None:
+                                        self.warn('Found additional thermo entry for species {0}'.format(label))
+                                    else:
+                                        species.thermo = thermo
+                                        species.composition = comp
+                                        species.note = note
                                 except KeyError:
                                     logging.info('Skipping unexpected species "{0}" while reading thermodynamics entry.'.format(label))
                                 thermo = []
diff --git a/test/data/duplicate-thermo.inp b/test/data/duplicate-thermo.inp
new file mode 100644
index 000000000..b1faacd53
--- /dev/null
+++ b/test/data/duplicate-thermo.inp
@@ -0,0 +1,32 @@
+Elements
+H  C
+END
+SPECIES
+foo bar baz
+END
+thermo
+    300.000  1000.000  5000.000
+foo                     C   1H   4          G   200.000  3500.000  1000.000    1
+ 7.48514950E-02 1.33909467E-02-5.73285809E-06 1.22292535E-09-1.01815230E-13    2
+-9.46834459E+03 1.84373180E+01 5.14987613E+00-1.36709788E-02 4.91800599E-05    3
+-4.84743026E-08 1.66693956E-11-1.02466476E+04-4.64130376E+00                   4
+bar                     C   1H   4          G   200.000  3500.000  1000.000    1
+ 7.48514950E-02 1.33909467E-02-5.73285809E-06 1.22292535E-09-1.01815230E-13    2
+-9.46834459E+03 1.84373180E+01 5.14987613E+00-1.36709788E-02 4.91800599E-05    3
+-4.84743026E-08 1.66693956E-11-1.02466476E+04-4.64130376E+00                   4
+baz                     C   1H   4          G   200.000  3500.000  1000.000    1
+ 7.48514950E-02 1.33909467E-02-5.73285809E-06 1.22292535E-09-1.01815230E-13    2
+-9.46834459E+03 1.84373180E+01 5.14987613E+00-1.36709788E-02 4.91800599E-05    3
+-4.84743026E-08 1.66693956E-11-1.02466476E+04-4.64130376E+00                   4
+! extra definition has different composition, which will trigger an exception
+! if this set of parameters are used.
+bar                     C   1H   6          G   200.000  3500.000  1000.000    1
+ 7.48514950E-02 1.33909467E-02-5.73285809E-06 1.22292535E-09-1.01815230E-13    2
+-9.46834459E+03 1.84373180E+01 5.14987613E+00-1.36709788E-02 4.91800599E-05    3
+-4.84743026E-08 1.66693956E-11-1.02466476E+04-4.64130376E+00                   4
+end
+
+reactions
+foo + bar = 2 baz      1.2345e12  1.0  200.0
+2foo + baz = 3bar      5.4321e10  1.0  500.0
+end
diff --git a/test/python/testConvert.py b/test/python/testConvert.py
index 71d654ed3..ffbb5f7af 100644
--- a/test/python/testConvert.py
+++ b/test/python/testConvert.py
@@ -100,6 +100,20 @@ class chemkinConverterTest(utilities.CanteraTest):
                                               outName='h2o2_missingThermo.cti',
                                               quiet=True))
 
+    def test_duplicate_thermo(self):
+        self.assertRaises(ck2cti.InputParseError,
+                          lambda: convertMech('../data/duplicate-thermo.inp',
+                                              outName='duplicate-thermo.cti',
+                                              quiet=True))
+
+        convertMech('../data/duplicate-thermo.inp',
+                    outName='duplicate-thermo.cti',
+                    quiet=True, permissive=True)
+
+        gas = ct.IdealGasMix('duplicate-thermo.cti')
+        self.assertTrue(gas.nSpecies(), 3)
+        self.assertTrue(gas.nReactions(), 2)
+
     def test_pathologicalSpeciesNames(self):
         convertMech('../data/species-names.inp',
                     outName='species-names.cti', quiet=True)