diff --git a/device/mcu.py b/device/mcu.py
index a875afe..21292dc 100644
--- a/device/mcu.py
+++ b/device/mcu.py
@@ -16,6 +16,7 @@
     McuCoherencyError,
     McuMagicError,
     McuMapVersionError,
+    McuProtocolError,
 )
 from .base import Device
 
@@ -256,6 +257,7 @@ class PowerFsmState(IntEnum):
     POWER_L5ON = 8
     POWER_L6ON = 9
     POWER_ON = 10
+    POWER_CONFIG = 11
 
 
 class PowerFlags(IntFlag):
@@ -593,7 +595,14 @@ def read_power(self, retries: int = 3,
             generation = self._read_u32(page, PowerReg.GENERATION)
             if generation & 1:
                 continue
-            fsm_state = PowerFsmState(self._read_u8(page, PowerReg.FSM_STATE))
+            raw_fsm_state = self._read_u8(page, PowerReg.FSM_STATE)
+            try:
+                fsm_state = PowerFsmState(raw_fsm_state)
+            except ValueError:
+                raise McuProtocolError(
+                    "unknown MCU power FSM state %d; firmware has a state that "
+                    "PowerFsmState does not -- update the enum" % raw_fsm_state
+                ) from None
             flags = PowerFlags(self._read_u8(page, PowerReg.FLAGS))
             live_pg_mask = self._read_u32(page, PowerReg.LIVE_PG_MASK)
             expected_pg_mask = self._read_u32(page, PowerReg.EXPECTED_PG_MASK)
diff --git a/tests/test_wire_contract.py b/tests/test_wire_contract.py
index 74d4345..21eccf3 100644
--- a/tests/test_wire_contract.py
+++ b/tests/test_wire_contract.py
@@ -173,6 +173,19 @@ def test_alarm_temp_device_enum_matches_firmware():
         assert int(mcu.AlarmTempDevice[name]) == index
 
 
+def test_power_fsm_state_enum_matches_firmware():
+    """PWR_OFF_STATE carries enum power_system_state, built from an X-macro list."""
+    with open(TASKS_H) as handle:
+        text = _strip_comments(handle.read())
+    text = re.sub(r"//.*", "", text)
+    match = re.search(r"#define\s+X_MACRO_PS_SYSTEM_STATES((?:[^\n]*\\\n)*[^\n]*)", text)
+    assert match, "X_MACRO_PS_SYSTEM_STATES not found in Tasks.h"
+    names = re.findall(r"X\(\s*([A-Za-z_][A-Za-z0-9_]*)\s*\)", match.group(1))
+    assert names == [member.name for member in mcu.PowerFsmState]
+    for index, name in enumerate(names):
+        assert int(mcu.PowerFsmState[name]) == index
+
+
 def test_config_write_clamps(defines):
     """Client and firmware must refuse the same values (the clamp is a safety control)."""
     assert _resolve("CFG_TEMP_MIN_C", defines) == mcu.ALARM_TEMP_MIN_C