diff --git a/releasenotes/notes/avoid-clashing-uids-e84ffe8132ce996d.yaml b/releasenotes/notes/avoid-clashing-uids-e84ffe8132ce996d.yaml
new file mode 100644
index 0000000..4ea18c6
--- /dev/null
+++ b/releasenotes/notes/avoid-clashing-uids-e84ffe8132ce996d.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fix a problem caused by failing to process multiple files with the
+    same UID portion of the filename. Ignore existing cases as long as
+    there is a corrective patch to remove them. Prevent new cases from
+    being introduced. See https://bugs.launchpad.net/reno/+bug/1688042
+    for details.
\ No newline at end of file
diff --git a/reno/scanner.py b/reno/scanner.py
index 95ceff6..e64fb97 100644
--- a/reno/scanner.py
+++ b/reno/scanner.py
@@ -150,6 +150,11 @@ class _ChangeAggregator(object):
     _delete_op = set([diff_tree.CHANGE_DELETE])
     _add_op = set([diff_tree.CHANGE_ADD])
 
+    def __init__(self):
+        # Track UIDs that had a duplication issue but have been
+        # deleted so we know not to throw an error for them.
+        self._deleted_bad_uids = set()
+
     def aggregate_changes(self, walk_entry, changes):
         sha = walk_entry.commit.id
         by_uid = collections.defaultdict(list)
@@ -216,15 +221,19 @@ class _ChangeAggregator(object):
                         (uid, diff_tree.CHANGE_DELETE, c[1], sha)
                         for c in changes
                     )
+                    self._deleted_bad_uids.add(uid)
                 elif types == self._add_op:
                     # There were multiple files in one commit using the
                     # same UID but different slugs. Warn the user about
                     # this case and then ignore the files. We allow delete
                     # (see above) to ensure they can be cleaned up.
                     msg = ('%s: found several files in one commit (%s)'
-                           ' with the same UID, ignoring them: %s' %
+                           ' with the same UID: %s' %
                            (uid, sha, [c[1] for c in changes]))
-                    LOG.warning(msg)
+                    if uid not in self._deleted_bad_uids:
+                        raise ValueError(msg)
+                    else:
+                        LOG.warning(msg)
                 else:
                     raise ValueError('Unrecognized changes: {!r}'.format(
                         changes))
diff --git a/reno/tests/test_scanner.py b/reno/tests/test_scanner.py
index 7e1a750..1e6b9bc 100644
--- a/reno/tests/test_scanner.py
+++ b/reno/tests/test_scanner.py
@@ -1798,14 +1798,16 @@ class AggregateChangesTest(Base):
             results,
         )
 
-    def test_add_multiple(self):
+    def test_add_multiple_after_delete(self):
         # Adding multiple files in one commit using the same UID but
-        # different slug causes the files to be ignored.
+        # different slug after we have seen a delete for the same UID
+        # causes the files to be ignored.
         entry = mock.Mock()
         n = self.get_note_num()
+        uid = '%016x' % n
         changes = []
         for i in range(2):
-            name = 'prefix/add%d-%016x.yaml' % (i, n)
+            name = 'prefix/add%d-%s.yaml' % (i, uid)
             entry.commit.id = 'commit-id'
             changes.append(
                 diff_tree.TreeChange(
@@ -1818,9 +1820,49 @@ class AggregateChangesTest(Base):
                     )
                 )
             )
+        # Set up the aggregator as though it had already seen a delete
+        # operation. Since the scan happens in reverse chronological
+        # order, the delete would have happened after the add, and we
+        # can ignore the files because the error has been corrected in
+        # a later patch.
+        self.aggregator._deleted_bad_uids.add(uid)
         results = list(self.aggregator.aggregate_changes(entry, changes))
         self.assertEqual([], results)
 
+    def test_add_multiple_without_delete(self):
+        # Adding multiple files in one commit using the same UID but
+        # different slug without a delete operation causes an
+        # exception.
+        entry = mock.Mock()
+        n = self.get_note_num()
+        uid = '%016x' % n
+        changes = []
+        for i in range(2):
+            name = 'prefix/add%d-%s.yaml' % (i, uid)
+            entry.commit.id = 'commit-id'
+            changes.append(
+                diff_tree.TreeChange(
+                    type=diff_tree.CHANGE_ADD,
+                    old=objects.TreeEntry(path=None, mode=None, sha=None),
+                    new=objects.TreeEntry(
+                        path=name.encode('utf-8'),
+                        mode='0222',
+                        sha='not-a-hash',
+                    )
+                )
+            )
+
+        # aggregate_changes() is a generator, so we have to wrap it in
+        # list() to process the data, so we need a little temporary
+        # function to do that and pass to assertRaises().
+        def get_results():
+            return list(self.aggregator.aggregate_changes(entry, changes))
+
+        self.assertRaises(
+            ValueError,
+            get_results,
+        )
+
     def test_delete(self):
         entry = mock.Mock()
         n = self.get_note_num()