diff --git a/interfaces/cython/cantera/ctml_writer.py b/interfaces/cython/cantera/ctml_writer.py
index 9fde1a57c..d69b76e61 100644
--- a/interfaces/cython/cantera/ctml_writer.py
+++ b/interfaces/cython/cantera/ctml_writer.py
@@ -390,7 +390,10 @@ def getAtomicComp(atoms):
     d = {}
     for t in toks:
         b = t.split(':')
-        d[b[0]] = int(b[1])
+        try:
+            d[b[0]] = int(b[1])
+        except ValueError:
+            d[b[0]] = float(b[1])
     return d
 
 def getReactionSpecies(s):
diff --git a/interfaces/cython/cantera/test/test_convert.py b/interfaces/cython/cantera/test/test_convert.py
index 0e1c83e61..6dc5a22ae 100644
--- a/interfaces/cython/cantera/test/test_convert.py
+++ b/interfaces/cython/cantera/test/test_convert.py
@@ -345,3 +345,8 @@ class CtmlConverterTest(utilities.CanteraTest):
             err = e
 
         self.assertIn('Multiply-declared species', err.args[0])
+
+    def test_noninteger_atomicity(self):
+        gas = ct.Solution('../data/noninteger-atomicity.cti')
+        self.assertNear(gas.molecular_weights[gas.species_index('CnHm')],
+                        10.65*gas.atomic_weight('C') + 21.8*gas.atomic_weight('H'))
diff --git a/test/data/noninteger-atomicity.cti b/test/data/noninteger-atomicity.cti
new file mode 100644
index 000000000..607b9b8ea
--- /dev/null
+++ b/test/data/noninteger-atomicity.cti
@@ -0,0 +1,67 @@
+units(length = "cm", time = "s", quantity = "mol", act_energy = "cal/mol")
+
+ideal_gas(name = "float",
+      elements = " O  H  C ",
+      species = """ O2  H2O  CO2 CnHm """,
+      reactions = "all",
+      initial_state = state(temperature = 300.0,
+                        pressure = OneAtm)    )
+
+
+species(name = "O2",
+    atoms = " O:2 ",
+    thermo = (
+       NASA( [  200.00,  1000.00], [  3.782456360E+00,  -2.996734160E-03,
+                9.847302010E-06,  -9.681295090E-09,   3.243728370E-12,
+               -1.063943560E+03,   3.657675730E+00] ),
+       NASA( [ 1000.00,  3500.00], [  3.282537840E+00,   1.483087540E-03,
+               -7.579666690E-07,   2.094705550E-10,  -2.167177940E-14,
+               -1.088457720E+03,   5.453231290E+00] )
+             )
+       )
+
+
+species(name = "H2O",
+    atoms = " H:2  O:1 ",
+    thermo = (
+       NASA( [  200.00,  1000.00], [  4.198640560E+00,  -2.036434100E-03,
+                6.520402110E-06,  -5.487970620E-09,   1.771978170E-12,
+               -3.029372670E+04,  -8.490322080E-01] ),
+       NASA( [ 1000.00,  3500.00], [  3.033992490E+00,   2.176918040E-03,
+               -1.640725180E-07,  -9.704198700E-11,   1.682009920E-14,
+               -3.000429710E+04,   4.966770100E+00] )
+             )
+       )
+
+species(name = "CO2",
+    atoms = " C:1  O:2 ",
+    thermo = (
+       NASA( [  200.00,  1000.00], [  2.356773520E+00,   8.984596770E-03,
+               -7.123562690E-06,   2.459190220E-09,  -1.436995480E-13,
+               -4.837196970E+04,   9.901052220E+00] ),
+       NASA( [ 1000.00,  3500.00], [  3.857460290E+00,   4.414370260E-03,
+               -2.214814040E-06,   5.234901880E-10,  -4.720841640E-14,
+               -4.875916600E+04,   2.271638060E+00] )
+             ),
+    transport = gas_transport(
+                     geom = "linear",
+                     diam =     3.76,
+                     well_depth =   244.00,
+                     polar =     2.65,
+                     rot_relax =     2.10),
+    note = "L 7/88"
+       )
+
+species(name = "CnHm",
+    atoms = " C:10.65  H:21.8 ",
+    thermo = (
+       NASA( [  300.00,  1000.00], [  9.335538100E-01,   2.642457900E-02,
+                6.105972700E-06,  -2.197749900E-08,   9.514925300E-12,
+               -1.395852000E+04,   1.920169100E+01] ),
+       NASA( [ 1000.00,  5000.00], [  7.534136800E+00,   1.887223900E-02,
+               -6.271849100E-06,   9.147564900E-10,  -4.783806900E-14,
+               -1.646751600E+04,  -1.789234900E+01] )
+             )
+       )
+
+reaction( "CnHm + 16.1 O2 => 10.65 CO2 + 10.9 H2O",   [3.16000E+07, 1.8, 934])