diff --git a/docs/model.rst b/docs/model.rst
index 8006d8e..23b024d 100644
--- a/docs/model.rst
+++ b/docs/model.rst
@@ -17,5 +17,7 @@ The :mod:`modelcif.model` Python module
 
 .. autoclass:: AbInitioModel
 
+.. autoclass:: NotModeledResidueRange
+
 .. autoclass:: ModelGroup
    :members:
diff --git a/modelcif/model.py b/modelcif/model.py
index 9876813..25d34d3 100644
--- a/modelcif/model.py
+++ b/modelcif/model.py
@@ -2,6 +2,8 @@
 import ihm.representation
 from ihm.model import Atom, ModelGroup  # noqa: F401
 import modelcif.data
+from ihm.util import _check_residue_range
+
 
 # Provide ma-specific docs for Atom
 if sys.version_info[0] >= 3:
@@ -62,10 +64,11 @@ def __init__(self, assembly, name=None):
             [ihm.representation.AtomicSegment(seg, rigid=False)
              for seg in assembly])
         self._atoms = []
-        # ModelCIF doesn't support not-modeled residue ranges, but python-ihm
-        # uses this information to populate the pdbx_poly_seq_scheme table,
-        # so add an empty range here
+
+        #: List of residue ranges that were explicitly not modeled. See
+        #: :class:`NotModeledResidueRange`.
         self.not_modeled_residue_ranges = []
+
         #: Quality scores for the model or part of it (a simple list of
         #: metric objects; see :mod:`modelcif.qa_metric`)
         self.qa_metrics = []
@@ -116,3 +119,20 @@ class AbInitioModel(Model):
     """
     model_type = "Ab initio model"
     other_details = None
+
+
+class NotModeledResidueRange(object):
+    """A range of residues that were explicitly not modeled.
+       See :attr:`Model.not_modeled_residue_ranges`.
+       These ranges are not explicitly stored in the mmCIF file,
+       but they will be excluded from the ``pdbx_poly_seq_scheme`` table.
+        
+       :param asym_unit: The asymmetric unit to which the residues belong.
+       :type asym_unit: :class:`~modelcif.AsymUnit`
+       :param int seq_id_begin: Starting residue in the range.
+       :param int seq_id_end: Ending residue in the range.
+    """
+    def __init__(self, asym_unit, seq_id_begin, seq_id_end):
+        self.asym_unit = asym_unit
+        self.seq_id_begin, self.seq_id_end = seq_id_begin, seq_id_end
+        _check_residue_range((seq_id_begin, seq_id_end), asym_unit.entity)
diff --git a/modelcif/reader.py b/modelcif/reader.py
index a13311d..298e1e1 100644
--- a/modelcif/reader.py
+++ b/modelcif/reader.py
@@ -663,7 +663,7 @@ def __call__(self, assembly_id, asym_id, seq_id_begin, seq_id_end):
         if seq_id_begin is None and seq_id_end is None:
             a.append(asym)
         else:
-            a.append(asym(int(seq_id_begin), int(seq_id_end), _check=False))
+            a.append(asym(int(seq_id_begin), int(seq_id_end)))
 
     def finalize(self):
         # Any AsymUnitRange which covers an entire asym,
@@ -899,7 +899,7 @@ def __call__(self, model_id, label_asym_id, label_seq_id, metric_id,
         model = self.sysr.models.get_by_id(model_id)
         asym = self.sysr.asym_units.get_by_id(label_asym_id)
         seq_id = self.get_int(label_seq_id)
-        residue = asym.residue(seq_id, _check=False)
+        residue = asym.residue(seq_id)
         metric_class = self.sysr.qa_by_id[metric_id]
         model.qa_metrics.append(metric_class(residue,
                                              self.get_float(metric_value)))
@@ -913,10 +913,10 @@ def __call__(self, model_id, label_asym_id_1, label_seq_id_1,
         model = self.sysr.models.get_by_id(model_id)
         asym1 = self.sysr.asym_units.get_by_id(label_asym_id_1)
         seq_id1 = self.get_int(label_seq_id_1)
-        residue1 = asym1.residue(seq_id1, _check=False)
+        residue1 = asym1.residue(seq_id1)
         asym2 = self.sysr.asym_units.get_by_id(label_asym_id_2)
         seq_id2 = self.get_int(label_seq_id_2)
-        residue2 = asym2.residue(seq_id2, _check=False)
+        residue2 = asym2.residue(seq_id2)
         metric_class = self.sysr.qa_by_id[metric_id]
         model.qa_metrics.append(metric_class(residue1, residue2,
                                              self.get_float(metric_value)))
diff --git a/modelcif/util/__init__.py b/modelcif/util/__init__.py
new file mode 100644
index 0000000..2ae2839
--- /dev/null
+++ b/modelcif/util/__init__.py
@@ -0,0 +1 @@
+pass
diff --git a/modelcif/util/make_mmcif.py b/modelcif/util/make_mmcif.py
new file mode 100644
index 0000000..9239385
--- /dev/null
+++ b/modelcif/util/make_mmcif.py
@@ -0,0 +1,93 @@
+#!/usr/bin/env python3
+
+"""
+Add minimal ModelCIF-related tables to an mmCIF file.
+
+Given any mmCIF file as input, this script will add any missing
+ModelCIF-related tables and write out a new file that is minimally compliant
+with the ModelCIF dictionary.
+
+This is done by simply reading in the original file with python-modelcif and
+then writing it out again, so
+  a) any data in the input file that is not understood by python-modelcif
+     will be lost on output; and
+  b) input files that aren't compliant with the PDBx dictionary, or that
+     contain syntax errors or other problems, may crash or otherwise confuse
+     python-modelcif.
+"""
+
+
+import modelcif.reader
+import modelcif.dumper
+import modelcif.model
+import ihm.util
+import os
+import argparse
+
+
+def add_modelcif_info(s):
+    if not s.title:
+        s.title = 'Auto-generated system'
+
+    for model_group in s.model_groups:
+        for model in model_group:
+            model.not_modeled_residue_ranges.extend(
+                _get_not_modeled_residues(model))
+    return s
+
+
+def _get_not_modeled_residues(model):
+    """Yield NotModeledResidueRange objects for all residue ranges in the
+       Model that are not referenced by Atom, Sphere, or pre-existing
+       NotModeledResidueRange objects"""
+    for assem in model.assembly:
+        asym = assem.asym if hasattr(assem, 'asym') else assem
+        if not asym.entity.is_polymeric():
+            continue
+        # Make a set of all residue indices of this asym "handled" either
+        # by being modeled (with Atom or Sphere objects) or by being
+        # explicitly marked as not-modeled
+        handled_residues = set()
+        for rr in model.not_modeled_residue_ranges:
+            if rr.asym_unit is asym:
+                for seq_id in range(rr.seq_id_begin, rr.seq_id_end + 1):
+                    handled_residues.add(seq_id)
+        for atom in model._atoms:
+            if atom.asym_unit is asym:
+                handled_residues.add(atom.seq_id)
+        # Convert set to a list of residue ranges
+        handled_residues = ihm.util._make_range_from_list(
+            sorted(handled_residues))
+        # Return not-modeled for each non-handled range
+        for r in ihm.util._invert_ranges(handled_residues,
+                                         end=assem.seq_id_range[1],
+                                         start=assem.seq_id_range[0]):
+            yield modelcif.model.NotModeledResidueRange(asym, r[0], r[1])
+
+
+def get_args():
+    p = argparse.ArgumentParser(
+        description="Add minimal ModelCIF-related tables to an mmCIF file.")
+    p.add_argument("input", metavar="input.cif", help="input mmCIF file name")
+    p.add_argument("output", metavar="output.cif",
+                   help="output mmCIF file name",
+                   default="output.cif", nargs="?")
+    return p.parse_args()
+
+
+def main():
+    args = get_args()
+
+    if (os.path.exists(args.input) and os.path.exists(args.output)
+            and os.path.samefile(args.input, args.output)):
+        raise ValueError("Input and output are the same file")
+
+    with open(args.input) as fh:
+        with open(args.output, 'w') as fhout:
+            modelcif.dumper.write(
+                fhout,
+                [add_modelcif_info(s) for s in modelcif.reader.read(fh)])
+
+
+if __name__ == '__main__':
+    main()
diff --git a/setup.py b/setup.py
index b66828d..24f2473 100755
--- a/setup.py
+++ b/setup.py
@@ -22,7 +22,7 @@
       author='Ben Webb',
       author_email='ben@salilab.org',
       url='https://github.com/ihmwg/python-modelcif',
-      packages=['modelcif'],
+      packages=['modelcif', 'modelcif.util'],
       install_requires=['ihm>=1.5'],
       classifiers=[
           "Programming Language :: Python :: 2.7",
diff --git a/test/input/no_title.cif b/test/input/no_title.cif
new file mode 100644
index 0000000..56db457
--- /dev/null
+++ b/test/input/no_title.cif
@@ -0,0 +1,3 @@
+data_PDBDEV_00000025
+_entry.id PDBDEV_00000025
+_struct.entry_id PDBDEV_00000025
diff --git a/test/input/not_modeled.cif b/test/input/not_modeled.cif
new file mode 100644
index 0000000..367ae17
--- /dev/null
+++ b/test/input/not_modeled.cif
@@ -0,0 +1,89 @@
+data_model
+#
+_exptl.method 'model, MODELLER Version 9.24 2020/08/21 11:54:31'
+#
+_modeller.version 9.24
+#
+loop_
+_struct_asym.id
+_struct_asym.entity_id
+_struct_asym.details
+A 1 ?
+B 2 ?
+#
+loop_
+_entity_poly_seq.entity_id
+_entity_poly_seq.num
+_entity_poly_seq.mon_id
+1 1 VAL
+1 2 GLY
+1 3 GLN
+1 4 GLN
+1 5 TYR
+1 6 SER
+1 7 SER
+2 1 ASP
+2 2 GLU
+#
+loop_
+_atom_site.group_PDB
+_atom_site.type_symbol
+_atom_site.label_atom_id
+_atom_site.label_alt_id
+_atom_site.label_comp_id
+_atom_site.label_asym_id
+_atom_site.auth_asym_id
+_atom_site.label_seq_id
+_atom_site.auth_seq_id
+_atom_site.pdbx_PDB_ins_code
+_atom_site.Cartn_x
+_atom_site.Cartn_y
+_atom_site.Cartn_z
+_atom_site.occupancy
+_atom_site.B_iso_or_equiv
+_atom_site.label_entity_id
+_atom_site.id
+_atom_site.pdbx_PDB_model_num
+ATOM N N . VAL A A 1 2 ? 115.846 27.965 -26.370 1.000 141.830 1 1 1
+ATOM C CA . VAL A A 1 2 ? 114.370 27.980 -26.088 1.000 143.490 1 2 1
+ATOM C C . VAL A A 1 2 ? 113.517 27.504 -27.287 1.000 143.910 1 3 1
+ATOM O O . VAL A A 1 2 ? 113.885 27.746 -28.441 1.000 146.600 1 4 1
+ATOM C CB . VAL A A 1 2 ? 113.901 29.406 -25.683 1.000 143.750 1 5 1
+ATOM C CG1 . VAL A A 1 2 ? 115.030 30.438 -25.931 1.000 144.590 1 6 1
+ATOM C CG2 . VAL A A 1 2 ? 112.669 29.783 -26.486 1.000 144.500 1 7 1
+ATOM N N . GLY A A 2 3 ? 112.371 26.869 -27.012 1.000 142.200 1 8 1
+ATOM C CA . GLY A A 2 3 ? 111.506 26.368 -28.075 1.000 137.530 1 9 1
+ATOM C C . GLY A A 2 3 ? 111.719 24.869 -28.275 1.000 135.820 1 10 1
+ATOM O O . GLY A A 2 3 ? 110.768 24.093 -28.268 1.000 134.380 1 11 1
+ATOM N N . GLN A A 3 4 ? 112.989 24.479 -28.392 1.000 134.310 1 12 1
+ATOM C CA . GLN A A 3 4 ? 113.468 23.113 -28.639 1.000 128.420 1 13 1
+ATOM C C . GLN A A 3 4 ? 113.556 22.956 -30.163 1.000 121.240 1 14 1
+ATOM O O . GLN A A 3 4 ? 113.552 23.977 -30.840 1.000 127.090 1 15 1
+ATOM C CB . GLN A A 3 4 ? 112.614 22.038 -27.919 1.000 132.340 1 16 1
+ATOM C CG . GLN A A 3 4 ? 113.028 21.943 -26.407 1.000 135.370 1 17 1
+ATOM C CD . GLN A A 3 4 ? 112.604 20.667 -25.677 1.000 138.260 1 18 1
+ATOM O OE1 . GLN A A 3 4 ? 112.836 19.543 -26.150 1.000 141.450 1 19 1
+ATOM N NE2 . GLN A A 3 4 ? 112.006 20.839 -24.497 1.000 139.310 1 20 1
+ATOM N N . GLN A A 4 5 ? 113.648 21.739 -30.710 1.000 124.970 1 21 1
+ATOM C CA . GLN A A 4 5 ? 113.808 21.534 -32.168 1.000 117.620 1 22 1
+ATOM C C . GLN A A 4 5 ? 114.778 22.519 -32.833 1.000 112.980 1 23 1
+ATOM O O . GLN A A 4 5 ? 114.677 23.727 -32.677 1.000 116.850 1 24 1
+ATOM C CB . GLN A A 4 5 ? 112.456 21.545 -32.905 1.000 121.870 1 25 1
+ATOM C CG . GLN A A 4 5 ? 111.763 20.153 -32.917 1.000 123.750 1 26 1
+ATOM C CD . GLN A A 4 5 ? 110.863 19.874 -34.145 1.000 123.650 1 27 1
+ATOM O OE1 . GLN A A 4 5 ? 110.040 20.712 -34.537 1.000 122.500 1 28 1
+ATOM N NE2 . GLN A A 4 5 ? 111.008 18.674 -34.737 1.000 122.090 1 29 1
+ATOM N N . SER A A 7 8 ? 117.999 25.245 -39.224 1.000 89.750 1 48 1
+ATOM C CA . SER A A 7 8 ? 119.165 25.590 -40.036 1.000 87.320 1 49 1
+ATOM C C . SER A A 7 8 ? 119.224 27.089 -40.277 1.000 84.820 1 50 1
+ATOM O O . SER A A 7 8 ? 120.074 27.594 -41.008 1.000 84.020 1 51 1
+ATOM C CB . SER A A 7 8 ? 119.112 24.859 -41.383 1.000 88.180 1 52 1
+ATOM O OG . SER A A 7 8 ? 117.956 25.221 -42.117 1.000 88.850 1 53 1
+ATOM N N . ASP B B 1 3 ? 71.339 57.678 52.031 1.000 152.010 2 54 1
+ATOM C CA . ASP B B 1 3 ? 70.427 58.819 51.717 1.000 152.390 2 55 1
+ATOM C C . ASP B B 1 3 ? 70.144 58.821 50.222 1.000 151.960 2 56 1
+ATOM O O . ASP B B 1 3 ? 70.984 59.245 49.435 1.000 151.590 2 57 1
+ATOM C CB . ASP B B 1 3 ? 71.083 60.142 52.119 1.000 153.250 2 58 1
+ATOM C CG . ASP B B 1 3 ? 71.660 60.105 53.526 1.000 154.120 2 59 1
+ATOM O OD1 . ASP B B 1 3 ? 72.652 59.371 53.741 1.000 154.200 2 60 1
+ATOM O OD2 . ASP B B 1 3 ? 71.119 60.804 54.415 1.000 154.250 2 61 1
diff --git a/test/input/struct_only.cif b/test/input/struct_only.cif
new file mode 100644
index 0000000..fd8617c
--- /dev/null
+++ b/test/input/struct_only.cif
@@ -0,0 +1,4 @@
+data_PDBDEV_00000025
+_entry.id PDBDEV_00000025
+_struct.entry_id PDBDEV_00000025
+_struct.title 'Architecture of Pol II(G) and molecular mechanism of transcription regulation by Gdown1'
diff --git a/test/test_make_mmcif.py b/test/test_make_mmcif.py
index e14c857..2b86065 100644
--- a/test/test_make_mmcif.py
+++ b/test/test_make_mmcif.py
@@ -7,34 +7,95 @@
 TOPDIR = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
 utils.set_search_paths(TOPDIR)
 import modelcif.reader
+import modelcif.util.make_mmcif  # Script should also be importable
 
 
-MAKE_MMCIF = os.path.join(TOPDIR, 'util', 'make-mmcif.py')
+MAKE_MMCIF = os.path.join(TOPDIR, 'modelcif', 'util', 'make_mmcif.py')
 
 
 class Tests(unittest.TestCase):
-    @unittest.skipIf(sys.version_info[0] < 3, "make-mmcif.py needs Python 3")
+    @unittest.skipIf(sys.version_info[0] < 3, "make_mmcif.py needs Python 3")
+    def test_simple(self):
+        """Simple test of make_mmcif utility script"""
+        incif = utils.get_input_file_name(TOPDIR, 'struct_only.cif')
+        subprocess.check_call([sys.executable, MAKE_MMCIF, incif])
+        with open('output.cif') as fh:
+            s, = modelcif.reader.read(fh)
+        self.assertEqual(s.title,
+                         'Architecture of Pol II(G) and molecular mechanism '
+                         'of transcription regulation by Gdown1')
+        os.unlink('output.cif')
+
+    @unittest.skipIf(sys.version_info[0] < 3, "make_mmcif.py needs Python 3")
+    def test_non_default_output(self):
+        """Simple test of make_mmcif with non-default output name"""
+        incif = utils.get_input_file_name(TOPDIR, 'struct_only.cif')
+        subprocess.check_call([sys.executable, MAKE_MMCIF, incif,
+                               'non-default-output.cif'])
+        with open('non-default-output.cif') as fh:
+            s, = modelcif.reader.read(fh)
+        self.assertEqual(s.title,
+                         'Architecture of Pol II(G) and molecular mechanism '
+                         'of transcription regulation by Gdown1')
+        os.unlink('non-default-output.cif')
+
+    @unittest.skipIf(sys.version_info[0] < 3, "make_mmcif.py needs Python 3")
+    def test_no_title(self):
+        """Check that make_mmcif adds missing title"""
+        incif = utils.get_input_file_name(TOPDIR, 'no_title.cif')
+        subprocess.check_call([sys.executable, MAKE_MMCIF, incif])
+        with open('output.cif') as fh:
+            s, = modelcif.reader.read(fh)
+        self.assertEqual(s.title, 'Auto-generated system')
+        os.unlink('output.cif')
+
+    @unittest.skipIf(sys.version_info[0] < 3, "make_mmcif.py needs Python 3")
     def test_bad_usage(self):
-        """Bad usage of make-mmcif utility script"""
+        """Bad usage of make_mmcif utility script"""
         ret = subprocess.call([sys.executable, MAKE_MMCIF])
+        self.assertEqual(ret, 2)
+
+    @unittest.skipIf(sys.version_info[0] < 3, "make_mmcif.py needs Python 3")
+    def test_same_file(self):
+        """Check that make_mmcif fails if input and output are the same"""
+        incif = utils.get_input_file_name(TOPDIR, 'struct_only.cif')
+        ret = subprocess.call([sys.executable, MAKE_MMCIF, incif, incif])
         self.assertEqual(ret, 1)
 
-    @unittest.skipIf(sys.version_info[0] < 3, "make-mmcif.py needs Python 3")
-    def test_mini(self):
-        """Check that make-mmcif works given only basic atom info"""
-        incif = utils.get_input_file_name(TOPDIR, 'mini.cif')
+    @unittest.skipIf(sys.version_info[0] < 3, "make_mmcif.py needs Python 3")
+    def test_not_modeled(self):
+        """Check addition of not-modeled residue information"""
+        incif = utils.get_input_file_name(TOPDIR, 'not_modeled.cif')
         subprocess.check_call([sys.executable, MAKE_MMCIF, incif])
         with open('output.cif') as fh:
-            s, = modelcif.reader.read(fh)
-        self.assertEqual(s.title, 'Auto-generated system')
-        self.assertEqual(len(s.protocols), 1)
-        p = s.protocols[0]
-        self.assertEqual(len(p.steps), 1)
-        step = p.steps[0]
-        self.assertIsInstance(step, modelcif.protocol.ModelingStep)
-        self.assertEqual(step.name, 'modeling')
-        self.assertEqual(step.input_data, [])
-        self.assertEqual(step.output_data, [])
+            contents = fh.readlines()
+        loop = contents.index("_pdbx_poly_seq_scheme.pdb_ins_code\n")
+        scheme = "".join(contents[loop-11:loop+11])
+        # Residues 5 and 6 in chain A, and 2 in chain B, are missing from
+        # atom_site, so should now be missing from the scheme table.
+        self.assertEqual(scheme, """#
+loop_
+_pdbx_poly_seq_scheme.asym_id
+_pdbx_poly_seq_scheme.entity_id
+_pdbx_poly_seq_scheme.seq_id
+_pdbx_poly_seq_scheme.mon_id
+_pdbx_poly_seq_scheme.pdb_seq_num
+_pdbx_poly_seq_scheme.auth_seq_num
+_pdbx_poly_seq_scheme.pdb_mon_id
+_pdbx_poly_seq_scheme.auth_mon_id
+_pdbx_poly_seq_scheme.pdb_strand_id
+_pdbx_poly_seq_scheme.pdb_ins_code
+A 1 1 VAL 2 2 VAL VAL A ?
+A 1 2 GLY 3 3 GLY GLY A ?
+A 1 3 GLN 4 4 GLN GLN A ?
+A 1 4 GLN 5 5 GLN GLN A ?
+A 1 5 TYR 5 ? ? ? A .
+A 1 6 SER 6 ? ? ? A .
+A 1 7 SER 8 8 SER SER A ?
+B 2 1 ASP 3 3 ASP ASP B ?
+B 2 2 GLU 2 ? ? ? B .
+#
+""")
         os.unlink('output.cif')