diff --git a/interfaces/cython/cantera/test/test_kinetics.py b/interfaces/cython/cantera/test/test_kinetics.py
index 0113dfe85..353e66111 100644
--- a/interfaces/cython/cantera/test/test_kinetics.py
+++ b/interfaces/cython/cantera/test/test_kinetics.py
@@ -462,3 +462,43 @@ class TestSofcKinetics(utilities.CanteraTest):
                              anode_bulk.electric_potential])
 
         self.compare(data, '../data/sofc-test.csv')
+
+
+class TestDuplicateReactions(utilities.CanteraTest):
+    infile = 'duplicate-reactions.cti'
+
+    def check(self, name):
+        with self.assertRaises(Exception) as cm:
+            ct.Solution(self.infile, name)
+        self.assertIn('duplicate reaction', str(cm.exception))
+
+    def test_forward_multiple(self):
+        self.check('A')
+
+    def test_opposite_direction1(self):
+        self.check('B')
+
+    def test_opposite_direction2(self):
+        self.check('C')
+
+    def test_opposite_direction3(self):
+        self.check('D')
+
+    def test_opposite_direction4(self):
+        gas = ct.Solution(self.infile, 'E')
+        self.assertEqual(gas.n_reactions, 2)
+
+    def test_common_efficiencies(self):
+        self.check('F')
+
+    def test_disjoint_efficiencies(self):
+        gas = ct.Solution(self.infile, 'G')
+        self.assertEqual(gas.n_reactions, 2)
+
+    def test_different_type(self):
+        gas = ct.Solution(self.infile, 'H')
+        self.assertEqual(gas.n_reactions, 2)
+
+    def test_declared_duplicate(self):
+        gas = ct.Solution(self.infile, 'I')
+        self.assertEqual(gas.n_reactions, 2)
diff --git a/src/kinetics/importKinetics.cpp b/src/kinetics/importKinetics.cpp
index d37bd809a..46ba2c7cc 100644
--- a/src/kinetics/importKinetics.cpp
+++ b/src/kinetics/importKinetics.cpp
@@ -1027,15 +1027,13 @@ bool rxninfo::installReaction(int iRxn, const XML_Node& rxnNode, Kinetics& kin,
         }
         for (size_t nn = 0; nn < rdata.products.size(); nn++) {
             rdata.net_stoich[int(rdata.products[nn])+1] += rdata.pstoich[nn];
-            participants += 1000000 * static_cast<unsigned long int>(rdata.products[nn]);
+            participants += static_cast<unsigned long int>(rdata.products[nn]);
         }
 
         vector<size_t>& related = m_participants[participants];
         for (size_t mm = 0; mm < related.size(); mm++) {
             ReactionData& other = *m_rdata[related[mm]];
-            if (rdata.reactants.size() != other.reactants.size()) {
-                continue; // different numbers of reactants
-            } else if (rdata.reactionType != other.reactionType) {
+            if (rdata.reactionType != other.reactionType) {
                 continue; // different reaction types
             } else if (rdata.duplicate && other.duplicate) {
                 continue; // marked duplicates
diff --git a/test/data/duplicate-reactions.cti b/test/data/duplicate-reactions.cti
new file mode 100644
index 000000000..0cb914912
--- /dev/null
+++ b/test/data/duplicate-reactions.cti
@@ -0,0 +1,59 @@
+units(length='cm', time='s', quantity='mol', act_energy='cal/mol')
+
+def make_gas(name, reactions):
+    ideal_gas(name=name,
+          elements=" O  H  Ar ",
+          species="""h2o2: H2  H  O  O2  OH  H2O  HO2  H2O2  AR """,
+          reactions=reactions,
+          transport="None")
+
+make_gas('A', 'A-*')
+make_gas('B', 'B-*')
+make_gas('C', 'C-*')
+make_gas('D', 'D-*')
+make_gas('E', 'E-*')
+make_gas('F', 'F-*')
+make_gas('G', 'G-*')
+make_gas('H', 'H-*')
+make_gas('I', 'I-*')
+
+kf = [1e10, 0, 100]
+
+# Forward multiple (not allowed)
+reaction('O + H2 <=> H + OH', kf, id='A-1')
+reaction('2 O + 2 H2 <=> 2 H + 2 OH', kf, id='A-2')
+
+# Opposite direction #1 (not allowed)
+reaction('O + H2 <=> H + OH', kf, id='B-1')
+reaction('H + OH <=> O + H2', kf, id='B-2')
+
+# Opposite direction #2 (not allowed)
+reaction('H + O2 + AR <=> HO2 + AR', kf, id='C-1')
+reaction('HO2 + AR <=> H + O2 + AR', kf, id='C-2')
+
+# Opposite direction #3 (not allowed)
+reaction('H + O2 + AR <=> HO2 + AR', kf, id='D-1')
+reaction('HO2 + AR => H + O2 + AR', kf, id='D-2')
+
+# Opposite direction #4 (allowed)
+reaction('H + O2 + AR => HO2 + AR', kf, id='E-1')
+reaction('HO2 + AR => H + O2 + AR', kf, id='E-2')
+
+# Common efficiencies (not allowed)
+falloff_reaction('2 OH (+ M) <=> H2O2 (+ M)', kf=kf, kf0=kf,
+                 efficiencies='H2:2.0 H2O:6.0', id='F-1')
+falloff_reaction('2 OH (+ M) <=> H2O2 (+ M)', kf=kf, kf0=kf,
+                 efficiencies='AR:0.7 H2:2.0', id='F-2')
+
+# Disjoint efficiencies (allowed)
+falloff_reaction('2 OH (+ H2O) <=> H2O2 (+ H2O)', kf=kf, kf0=kf, id='G-1')
+falloff_reaction('2 OH (+ M) <=> H2O2 (+ M)', kf=kf, kf0=kf,
+                 efficiencies='AR:0.7 H2:2.0 H2O:0.0', id='G-2')
+
+# Different reaction type (allowed)
+reaction('O + H2 <=> H + OH', kf, id='H-1')
+three_body_reaction('O + H2 + M <=> H + OH + M', kf, id='H-2')
+
+# Declared duplicate (allowed)
+reaction('O + H2 <=> H + OH', kf, options='duplicate', id='I-1')
+reaction('H + OH <=> O + H2', kf, options='duplicate', id='I-2')