diff --git a/hydra/install_storage.py b/hydra/install_storage.py
index c35d5e3..f22f5dd 100644
--- a/hydra/install_storage.py
+++ b/hydra/install_storage.py
@@ -118,6 +118,14 @@ def partition_plan(request, probe, topo):
         fail('ESP must be an existing FAT GPT EFI System Partition')
     if not UUID.fullmatch(esp_node.get('uuid') or ''):
         fail('ESP filesystem UUID missing')
+    # fstab resolves the ESP by filesystem UUID. Copies on any surviving
+    # device are ambiguous even when their GPT partition identities differ.
+    # Root's old filesystem is replaced before fstab is written.
+    copies = [path for path, node in topo.nodes.items()
+              if path not in {root, esp}
+              and (node.get('uuid') or '').lower() == esp_node['uuid'].lower()]
+    if copies:
+        fail('ESP filesystem UUID is ambiguous on surviving devices: ' + ', '.join(sorted(copies)))
     # Equal GPT IDs anywhere would make later PARTUUID recovery ambiguous.
     ids = [n.get('partuuid', '').lower() for n in topo.nodes.values() if n.get('partuuid')]
     if len(ids) != len(set(ids)):
diff --git a/tests/test_installer.py b/tests/test_installer.py
index 14c7ecf..847033c 100644
--- a/tests/test_installer.py
+++ b/tests/test_installer.py
@@ -108,6 +108,23 @@ class PartitionGuardTests(unittest.TestCase):
     def test_explicit_partitions_allow_unrelated_mounted_sibling(self):
         self.assertEqual(i.validate_request(partition_request(), FakeProbe(partition_topology(sibling_mounted=True))), '/dev/vda2')
 
+    def test_duplicate_esp_uuid_on_surviving_devices_is_refused(self):
+        for location in ('sibling', 'other-disk'):
+            for copied_uuid in ('ABCD-1234', 'abcd-1234'):
+                topo = partition_topology()
+                if location == 'sibling':
+                    copied = topo.nodes['/dev/vda3']
+                else:
+                    copied = disk('/dev/vdb1', kind='part', pkname='/dev/vdb')
+                    copied.update(start=2048, size=1024**3,
+                                  partuuid='bbbbbbbb-cccc-dddd-eeee-000000000001')
+                    topo = topology(topo.nodes['/dev/vda'], disk('/dev/vdb', children=[copied]))
+                    copied = topo.nodes['/dev/vdb1']
+                copied.update(fstype='vfat', uuid=copied_uuid,
+                              parttype='c12a7328-f81f-11d2-ba4b-00a0c93ec93b')
+                with self.subTest(location=location, uuid=copied_uuid), self.assertRaisesRegex(i.InstallError, 'ESP filesystem UUID'):
+                    i.validate_request(partition_request(), FakeProbe(topo))
+
     def test_modes_and_confirmations_are_unambiguous(self):
         for changes in ({'disk': '/dev/vda'}, {'esp_partition': None}, {'root_fs': 'xfs'},
                         {'confirm_erase': '/dev/vda'}, {'confirm_format': '/dev/vda3', 'execute': True}):
@@ -251,6 +268,17 @@ class PartitionPipelineTests(unittest.TestCase):
     def install(self, runner):
         i.install(self.request, runner, self.probe, self.root, 'test-password', io.StringIO())
 
+    def test_duplicate_fat_uuid_with_distinct_partuuid_stops_before_root_format(self):
+        copied = self.probe.topo.nodes['/dev/vda3']
+        copied.update(fstype='vfat', uuid='ABCD-1234',
+                      parttype='c12a7328-f81f-11d2-ba4b-00a0c93ec93b')
+        self.assertNotEqual(copied['partuuid'], self.probe.topo.nodes['/dev/vda1']['partuuid'])
+        runner = FakeRunner(self.root)
+        with self.assertRaisesRegex(i.InstallError, 'ESP filesystem UUID'):
+            self.install(runner)
+        self.assertEqual(runner.calls, [])
+        self.assertFalse((self.root/'etc/fstab').exists())
+
     def test_existing_mode_formats_root_only_and_records_owned_layout(self):
         runner = FakeRunner(self.root)
         self.install(runner)