diff --git a/esphome_device_builder/controllers/_device_mqtt_coordinator.py b/esphome_device_builder/controllers/_device_mqtt_coordinator.py
index 8043e819..629b5e21 100644
--- a/esphome_device_builder/controllers/_device_mqtt_coordinator.py
+++ b/esphome_device_builder/controllers/_device_mqtt_coordinator.py
@@ -16,6 +16,8 @@
 from typing import Any
 
 import yaml
+from esphome import yaml_util
+from esphome.core import EsphomeError
 
 from ..helpers.device_yaml import load_device_yaml
 from ..helpers.yaml import FastestSafeLoader
@@ -299,12 +301,29 @@ def _load_secrets(config_dir: Path) -> dict[str, Any]:
             # equivalent of SafeLoader. Same noqa rationale as the
             # ``_TolerantYamlLoader`` call above.
             data = yaml.load(f, Loader=FastestSafeLoader)  # noqa: S506
-    except yaml.YAMLError:
-        _LOGGER.warning("Could not parse secrets.yaml — MQTT broker secrets unavailable")
-        return {}
+    except (yaml.YAMLError, OSError):
+        # A plain secrets.yaml is key/value scalars the fast loader
+        # handles. ESPHome tags (``!include`` / ``!secret``) and merge
+        # keys are not — the documented HA-shared
+        # ``<<: !include ../secrets.yaml`` pattern lands here. Retry with
+        # ESPHome's loader, which resolves them the way a compile does.
+        data = _load_secrets_via_esphome(secrets_path)
     return data if isinstance(data, dict) else {}
 
 
+def _load_secrets_via_esphome(secrets_path: Path) -> dict[str, Any] | None:
+    """Load *secrets_path* with ESPHome's loader (``!include`` / merge keys)."""
+    try:
+        data = yaml_util.load_yaml(secrets_path)
+    except (EsphomeError, yaml.YAMLError, OSError):
+        _LOGGER.warning("Could not parse secrets.yaml — MQTT broker secrets unavailable")
+        return None
+    if not isinstance(data, dict):
+        _LOGGER.warning("Could not parse secrets.yaml — MQTT broker secrets unavailable")
+        return None
+    return data
+
+
 def _safe_mtime(path: Path) -> float:
     """Return *path*'s mtime, or ``0.0`` when the file is missing."""
     try:
diff --git a/tests/test_mqtt_monitor.py b/tests/test_mqtt_monitor.py
index 9759e66d..3e1dc5b1 100644
--- a/tests/test_mqtt_monitor.py
+++ b/tests/test_mqtt_monitor.py
@@ -302,6 +302,52 @@ async def test_coordinator_resolves_secrets_from_secrets_yaml(
     assert stub_monitor.instances[0].broker.password == "shh"
 
 
+async def test_coordinator_resolves_secrets_via_included_secrets_file(
+    tmp_path: Path,
+    stub_monitor: type[_RecordingMonitor],
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    # secrets.yaml pulls in a shared file via the merge-key +
+    # ``!include`` pattern (HA-shared secrets); the plain SafeLoader
+    # rejects it, so the ESPHome-loader fallback must resolve it.
+    (tmp_path / "shared.yaml").write_text("mqtt_broker: 10.0.0.9\nmqtt_pw: shh\n")
+    (tmp_path / "secrets.yaml").write_text("<<: !include shared.yaml\n")
+    devices = [
+        _write_device(
+            tmp_path,
+            "alpha",
+            "mqtt:\n  broker: !secret mqtt_broker\n  password: !secret mqtt_pw\n",
+        )
+    ]
+    coord = _make_coordinator(tmp_path, devices)
+    with caplog.at_level("WARNING"):
+        await coord.reconcile()
+    assert coord.active_brokers == 1
+    assert stub_monitor.instances[0].broker.host == "10.0.0.9"
+    assert stub_monitor.instances[0].broker.password == "shh"
+    assert "Could not parse secrets.yaml" not in caplog.text
+
+
+async def test_coordinator_warns_when_secrets_unparseable_by_both_loaders(
+    tmp_path: Path,
+    stub_monitor: type[_RecordingMonitor],
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    (tmp_path / "secrets.yaml").write_text("<<: !include does_not_exist.yaml\n")
+    devices = [
+        _write_device(
+            tmp_path,
+            "alpha",
+            "mqtt:\n  broker: !secret mqtt_broker\n",
+        )
+    ]
+    coord = _make_coordinator(tmp_path, devices)
+    with caplog.at_level("WARNING"):
+        await coord.reconcile()
+    assert coord.active_brokers == 0
+    assert "Could not parse secrets.yaml" in caplog.text
+
+
 async def test_coordinator_resolves_broker_pulled_in_via_packages(
     tmp_path: Path,
     stub_monitor: type[_RecordingMonitor],