diff --git a/openff/interchange/_tests/unit_tests/interop/gromacs/export/test_export.py b/openff/interchange/_tests/unit_tests/interop/gromacs/export/test_export.py
index fbfcaca1..dea1935c 100644
--- a/openff/interchange/_tests/unit_tests/interop/gromacs/export/test_export.py
+++ b/openff/interchange/_tests/unit_tests/interop/gromacs/export/test_export.py
@@ -193,6 +193,29 @@ def test_atom_names_pdb(self):
 
         assert openmm_atom_names == pdb_atom_names
 
+    def test_residue_id_increment(self):
+        """Test that residue IDs increment properly for multiple molecules."""
+
+        mol1 = MoleculeWithConformer.from_smiles("CCO")
+        mol2 = MoleculeWithConformer.from_smiles("CCO")
+
+        for atom in mol1.atoms:
+            atom.metadata["residue_name"] = "MOL1"
+        for atom in mol2.atoms:
+            atom.metadata["residue_name"] = "MOL2"
+
+        interchange = Interchange.from_smirnoff(
+            ForceField("openff-2.0.0.offxml"), [mol1, mol2]
+        )
+        interchange.to_gro("resid.gro")
+
+        with open("resid.gro") as gro_file:
+            lines = gro_file.readlines()
+            residue_ids = {int(line[:5].strip()) for line in lines[2:-2]}
+
+            # expecting residue IDs 1 and 2 for MOL1 and MOL2 respectively
+            assert residue_ids == {1, 2}
+
 
 class TestGROMACS(_NeedsGROMACS):
     @pytest.mark.slow
diff --git a/openff/interchange/interop/gromacs/export/_export.py b/openff/interchange/interop/gromacs/export/_export.py
index e16f375b..f031d6ca 100644
--- a/openff/interchange/interop/gromacs/export/_export.py
+++ b/openff/interchange/interop/gromacs/export/_export.py
@@ -445,6 +445,7 @@ def _write_gro(self, gro, decimal: int):
         gro.write(f"{n_particles}\n")
 
         count = 0
+        residue_id = 1
         for molecule_name, molecule in self.system.molecule_types.items():
             n_copies = self.system.molecules[molecule_name]
 
@@ -456,7 +457,8 @@ def _write_gro(self, gro, decimal: int):
                         f"%{decimal + 5}.{decimal}f"
                         f"%{decimal + 5}.{decimal}f\n"
                         % (
-                            atom.residue_index,  # This needs to be looked up from a different data structure
+                            residue_id = 1,
+                            # (hidden: 1013) atom.residue_index,  # This needs to be looked up from a different data structure
                             atom.residue_name[:5],
                             atom.name[:5],
                             (count + 1) % 100000,
@@ -467,6 +469,7 @@ def _write_gro(self, gro, decimal: int):
                     )
 
                     count += 1
+                residue_id += 1
 
         if self.system.box is None:
             warnings.warn(