diff --git a/custom_components/nvidia_shield/config_flow.py b/custom_components/nvidia_shield/config_flow.py
index 4e5cf8d..ea4c78b 100644
--- a/custom_components/nvidia_shield/config_flow.py
+++ b/custom_components/nvidia_shield/config_flow.py
@@ -370,6 +370,19 @@ class NvidiaShieldConfigFlow(config_entries.ConfigFlow, domain=DOMAIN):
                     )
                 return self.async_abort(reason="already_configured")
             self._abort_if_unique_id_configured()
+        else:
+            # t32 F2 (review rider): MAC-less discovery cannot carry a
+            # unique_id — HA's helper records the uniqueness-less discovery
+            # (the same discovery context can't stack duplicates) and the
+            # host guard keeps a second discovery of an already-configured
+            # host from stacking another prefill.
+            self._async_handle_discovery_without_unique_id()
+            for entry in self._async_current_entries():
+                existing_host = entry.options.get(
+                    CONF_PROTOCOL_HOST
+                ) or entry.options.get(CONF_ADB_HOST)
+                if existing_host and existing_host == host:
+                    return self.async_abort(reason="already_configured")
 
         # First-time setup: pre-filled user step
         return await self.async_step_user()
@@ -490,7 +503,7 @@ class NvidiaShieldConfigFlow(config_entries.ConfigFlow, domain=DOMAIN):
 
         # duplicate guards
         yhost = block.get(CONF_ADB_HOST) or block.get(CONF_PROTOCOL_HOST)
-        for existing in self.hass.config_entries.async_entries():
+        for existing in self._async_current_entries():
             ehost = existing.options.get(CONF_PROTOCOL_HOST) or existing.options.get(
                 CONF_ADB_HOST
             )
diff --git a/tests/entity_stublib.py b/tests/entity_stublib.py
index 2cee30d..19d6c73 100644
--- a/tests/entity_stublib.py
+++ b/tests/entity_stublib.py
@@ -144,6 +144,10 @@ def install() -> None:
         async_set_unique_id = _stub_set_unique_id
         _abort_if_unique_id_configured = _noop_abort
 
+        def _async_handle_discovery_without_unique_id(self):
+            # t32 F2 (audited helper): recording no-op at hub scope
+            pass
+
         def async_show_form(self, *, step_id, data_schema=None, errors=None):
             return {
                 "type": "form",
diff --git a/tests/test_init.py b/tests/test_init.py
index c0386ea..8aed762 100644
--- a/tests/test_init.py
+++ b/tests/test_init.py
@@ -223,6 +223,9 @@ class TestImportStep:
             **kwargs,
         }
         flow.async_abort = lambda **kwargs: {"type": "abort", **kwargs}
+        flow._async_current_entries = lambda: list(
+            hass.config_entries.async_entries()
+        )
         return flow
 
     async def test_ui_configured_host_never_re_seeded(self):
diff --git a/tests/test_standalone_setup.py b/tests/test_standalone_setup.py
index 8bda98e..1d70176 100644
--- a/tests/test_standalone_setup.py
+++ b/tests/test_standalone_setup.py
@@ -95,6 +95,12 @@ def _install_stubs() -> None:
         def _async_current_entries(self):
             return _zc_holder.entries
 
+        # t32 F2: the audited helper for uniqueness-less discovery — a
+        # recording no-op here; the flow's own host guard does the stacking
+        # prevention the acceptance pins.
+        def _async_handle_discovery_without_unique_id(self):
+            _zc_holder.discovery_without_unique_id_calls += 1
+
     class OptionsFlow:
         def async_show_form(self, *, step_id, data_schema=None, errors=None):
             return {
@@ -128,7 +134,7 @@ def _install_stubs() -> None:
 
     # Shared holder so tests can swap the current-entry list through the
     # module object (the stub closure reads this same object).
-    _zc_holder = types.SimpleNamespace(entries=[])
+    _zc_holder = types.SimpleNamespace(entries=[], discovery_without_unique_id_calls=0)
     sys.modules[__name__]._zc_holder = _zc_holder
 
     class AbortIfConfiguredError(Exception):
@@ -835,6 +841,50 @@ class TestIpChangeSelfHealF1:
             assert factory() is None
 
 
+class TestMacLessDiscoveryF2:
+    """t32 F2 (rider): MAC-less zeroconf discovery records the
+    uniqueness-less discovery and can't stack a duplicate prefill."""
+
+    def _discovery(self, host="192.168.1.50", props=None):
+        return SimpleNamespace(
+            ip_address=host, host=host, properties=props or {}
+        )
+
+    async def test_mac_less_records_the_helper(self, tmp_path):
+        module = _form_module()
+        flow = module.NvidiaShieldConfigFlow()
+        flow.hass = FakeHass(str(tmp_path))
+        sys.modules[__name__]._zc_holder.discovery_without_unique_id_calls = 0
+
+        result = await flow.async_step_zeroconf(self._discovery())
+
+        assert result["type"] == "form"  # prefill still offered once
+        assert (
+            sys.modules[__name__]._zc_holder.discovery_without_unique_id_calls
+            == 1
+        )
+
+    async def test_mac_less_rediscovery_does_not_stack(self, tmp_path):
+        """A second MAC-less discovery of an already-configured host
+        aborts — one-entry outcome."""
+        module = _form_module()
+        flow = module.NvidiaShieldConfigFlow()
+        flow.hass = FakeHass(str(tmp_path))
+        entry = SimpleNamespace(
+            entry_id="e1",
+            unique_id=None,  # MAC-less entry
+            options={CONF_PROTOCOL_HOST: "192.168.1.50"},
+            title="Shield",
+        )
+        sys.modules[__name__]._zc_holder.entries[:] = [entry]
+
+        result = await flow.async_step_zeroconf(self._discovery())
+
+        assert result == {"type": "abort", "reason": "already_configured"}
+        # the entries list is untouched: one-entry outcome
+        assert len(sys.modules[__name__]._zc_holder.entries) == 1
+
+
 class TestZeroconfDiscovery:
     """P4-1a: _androidtvremote2._tcp discovery → pre-filled user step."""