diff --git a/arc/statmech/arkane.py b/arc/statmech/arkane.py
index 9f6d530ce9..6122affcbd 100644
--- a/arc/statmech/arkane.py
+++ b/arc/statmech/arkane.py
@@ -343,9 +343,18 @@ def render_arkane_input_template(self,
             skip_rotors (bool, optional): Whether to skip internal rotor consideration. Default: ``False``.
             e0_only (bool, optional): Whether to only run statmech (w/o thermo) to compute E0. Default: ``False``.
         """
+        reaction_species_labels = set()
+        for rxn in self.reactions or list():
+            reactants, products = rxn.get_reactants_and_products(return_copies=False)
+            rxn.reactants = [spc.label for spc in reactants]
+            rxn.products = [spc.label for spc in products]
+            reaction_species_labels.update(rxn.reactants + rxn.products)
         species_list = list()
         for spc in self.species:
-            if e0_only or spc.compute_thermo:
+            # A species named by a reaction must be declared even when its thermo is not being
+            # computed: Arkane's reaction() references species by label from the declared-species
+            # dict, so an undeclared reactant/product raises KeyError and no rate is produced.
+            if e0_only or spc.compute_thermo or spc.label in reaction_species_labels:
                 smiles = spc.mol.copy(deep=True).to_smiles() if not spc.is_ts else ''
                 adjlist = ''
                 if smiles:
@@ -387,11 +396,6 @@ def render_arkane_input_template(self,
 
         freq_scale_factor = f'\nfrequencyScaleFactor = {self.freq_scale_factor}' \
             if self.freq_scale_factor is not None else ''
-        if self.reactions is not None:
-            for rxn in self.reactions:
-                reactants, products = rxn.get_reactants_and_products()
-                rxn.reactants = [spc.label for spc in reactants]
-                rxn.products = [spc.label for spc in products]
         calc_type = 'kinetics' if self.reactions else 'thermo'
         return Template(main_input_template).render(
             title=f'Arkane {calc_type} calculation',
diff --git a/arc/statmech/arkane_test.py b/arc/statmech/arkane_test.py
index 2afd612d23..a724f49eb4 100644
--- a/arc/statmech/arkane_test.py
+++ b/arc/statmech/arkane_test.py
@@ -471,6 +471,25 @@ def test_lone_pair_species_uses_adjacency_list(self):
         self.assertNotIn("SMILES('[CH2]')", content)     # must NOT use the lossy SMILES
         self.assertIn("structure=SMILES('O')", content)  # normal species unchanged
 
+    def test_kinetics_input_declares_reaction_species_without_compute_thermo(self):
+        """A reactant/product carrying ``compute_thermo=False`` must still be declared as a
+        ``species(...)`` line in a rendered kinetics input. Otherwise the ``reaction(...)`` block
+        references a species Arkane never declared, and Arkane raises ``KeyError`` on the label
+        (``arkane/input.py`` builds ``reactants`` from the declared-species dict). A species that no
+        reaction names must still be excluded by ``compute_thermo=False``."""
+        rxn = ARCReaction(r_species=[ARCSpecies(label='R', smiles='C[NH]', compute_thermo=False)],
+                          p_species=[ARCSpecies(label='P', smiles='[CH2]N', compute_thermo=False)])
+        rxn.ts_species = ARCSpecies(label='TS', is_ts=True)
+        spc_x = ARCSpecies(label='X', smiles='O', compute_thermo=False)
+        adapter = ArkaneAdapter(output_directory=self.tmpdir, calcs_directory=self.tmpdir,
+                                output_dict=dict(), sp_level=Level('gfn2'),
+                                species=rxn.r_species + rxn.p_species + [rxn.ts_species, spc_x],
+                                reactions=[rxn])
+        content = adapter.render_arkane_input_template(statmech_dir=self.tmpdir)
+        self.assertIn("species('R',", content)
+        self.assertIn("species('P',", content)
+        self.assertNotIn("species('X',", content)
+
     @classmethod
     def tearDownClass(cls):
         """