diff --git a/octodns/manager.py b/octodns/manager.py
index 566b979..40a9c4f 100644
--- a/octodns/manager.py
+++ b/octodns/manager.py
@@ -315,12 +315,13 @@ class Manager(object):
             while zones:
                 # Grab the one we'lre going to work on now
                 zone = zones.pop()
-                trimmer = len(zone) + 1
+                dotted = f'.{zone}'
+                trimmer = len(dotted)
                 subs = set()
                 # look at all the zone names that come after it
                 for candidate in zones:
-                    # If they end with this zone's name them they're a sub
-                    if candidate.endswith(zone):
+                    # If they end with this zone's dotted name, it's a sub
+                    if candidate.endswith(dotted):
                         # We want subs to exclude the zone portion
                         subs.add(candidate[:-trimmer])
 
diff --git a/tests/test_octodns_manager.py b/tests/test_octodns_manager.py
index e3a5a50..420dfe3 100644
--- a/tests/test_octodns_manager.py
+++ b/tests/test_octodns_manager.py
@@ -776,6 +776,17 @@ class TestManager(TestCase):
             set(), manager.configured_sub_zones('skipped.alevel.unit2.tests.')
         )
 
+        # zones that end with names of others
+        manager.config['zones'] = {
+            'unit.tests.': {},
+            'uunit.tests.': {},
+            'uuunit.tests.': {},
+        }
+        manager._configured_sub_zones = None
+        self.assertEqual(set(), manager.configured_sub_zones('unit.tests.'))
+        self.assertEqual(set(), manager.configured_sub_zones('uunit.tests.'))
+        self.assertEqual(set(), manager.configured_sub_zones('uuunit.tests.'))
+
 
 class TestMainThreadExecutor(TestCase):
     def test_success(self):