diff --git a/custom_components/zaptec/sensor.py b/custom_components/zaptec/sensor.py
index 5d77e25..f219ac7 100644
--- a/custom_components/zaptec/sensor.py
+++ b/custom_components/zaptec/sensor.py
@@ -111,14 +111,20 @@ def _update_from_zaptec(self) -> None:
         # are OCMF (Open Charge Metering Format) data structures and must be
         # parsed to get the latest reading.
 
-        # Ge the two OCMF data structures from Zaptec. The first one must exists,
+        # Get the two OCMF data structures from Zaptec. The first one must exists,
         # the second one is optional.
         meter_value = self._get_zaptec_value(key="signed_meter_value")
         session = self._get_zaptec_value(key="completed_session", default={})
 
         # Get the latest energy reading from both and use the largest value
         reading = get_ocmf_max_reader_value(meter_value)
-        session_reading = get_ocmf_max_reader_value(session.get("SignedSession", {}))
+        if isinstance(session, dict):
+            session_reading = get_ocmf_max_reader_value(session.get("SignedSession", {}))
+        else:
+            _LOGGER.debug(
+                "Incorrect typing for completed_session: %s", type(session).__qualname__
+            )
+            session_reading = 0.0
 
         self._attr_native_value = max(reading, session_reading)
         self._attr_available = True
diff --git a/custom_components/zaptec/zaptec/zconst.py b/custom_components/zaptec/zaptec/zconst.py
index b268a48..dc8e79a 100644
--- a/custom_components/zaptec/zaptec/zconst.py
+++ b/custom_components/zaptec/zaptec/zconst.py
@@ -182,6 +182,8 @@ def type_network_type(self, val: int) -> str:
     def type_ocmf(self, data: str) -> dict[str, Any]:
         """Open Charge Metering Format (OCMF) type."""
         # https://github.com/SAFE-eV/OCMF-Open-Charge-Metering-Format/blob/master/OCMF-en.md
+        if not data:
+            return {}
         sects = data.split("|")
         if len(sects) not in (2, 3) or sects[0] != "OCMF":
             raise ValueError(f"Invalid OCMF data: {data}")
diff --git a/tests/zaptec/test_zconst.py b/tests/zaptec/test_zconst.py
index 80522c8..93e3ae2 100644
--- a/tests/zaptec/test_zconst.py
+++ b/tests/zaptec/test_zconst.py
@@ -173,6 +173,52 @@ def test_completed_session() -> None:
     assert ZCONST.type_completed_session(completed_session) == expected_completed_session_dict
 
 
+def test_completed_session_corrupted_or_no_signed_session() -> None:
+    """Test type conversion for completed_session if there is a corrupted or no signed session."""
+
+    expected_energy = 27.432
+    completed_session_signed_is_null = (
+        r'{"SessionId":"01234567-89ab-cdef-0123-456789abcdef","Energy":27.432,"StartDateTime":'
+        r'"2025-08-28T15:02:55.188048Z","EndDateTime":"2025-09-01T10:32:50.517055Z",'
+        r'"ReliableClock":true,"StoppedByRFID":false,"AuthenticationCode":"",'
+        r'"FirstAuthenticatedDateTime":"","SignedSession":null}'
+    )
+    res_signed_is_null = ZCONST.type_completed_session(completed_session_signed_is_null)
+    assert res_signed_is_null.get("Energy") == expected_energy
+
+    completed_session_signed_is_empty = (
+        r'{"SessionId":"01234567-89ab-cdef-0123-456789abcdef","Energy":27.432,"StartDateTime":'
+        r'"2025-08-28T15:02:55.188048Z","EndDateTime":"2025-09-01T10:32:50.517055Z",'
+        r'"ReliableClock":true,"StoppedByRFID":false,"AuthenticationCode":"",'
+        r'"FirstAuthenticatedDateTime":"","SignedSession":""}'
+    )
+    res_signed_is_empty = ZCONST.type_completed_session(completed_session_signed_is_empty)
+    assert res_signed_is_empty.get("Energy") == expected_energy
+
+    completed_session_no_signed = (
+        r'{"SessionId":"01234567-89ab-cdef-0123-456789abcdef","Energy":27.432,"StartDateTime":'
+        r'"2025-08-28T15:02:55.188048Z","EndDateTime":"2025-09-01T10:32:50.517055Z",'
+        r'"ReliableClock":true,"StoppedByRFID":false,"AuthenticationCode":"",'
+        r'"FirstAuthenticatedDateTime":""}'
+    )
+    res_no_signed = ZCONST.type_completed_session(completed_session_no_signed)
+    assert res_no_signed.get("Energy") == expected_energy
+
+    completed_session_signed_invalid_ocmf = (  # OMCF instead of OCMF
+        r'{"SessionId":"01234567-89ab-cdef-0123-456789abcdef","Energy":27.432,"StartDateTime":'
+        r'"2025-08-28T15:02:55.188048Z","EndDateTime":"2025-09-01T10:32:50.517055Z",'
+        r'"ReliableClock":true,"StoppedByRFID":false,"AuthenticationCode":"",'
+        r'"FirstAuthenticatedDateTime":"","SignedSession":"OMCF|{\"FV\":\"1.0\",\"GI\":'
+        r"\"ZAPTEC GO\",\"GS\":\"ZAP000042\",\"GV\":\"2.4.2.4\",\"PG\":\"T1\",\"RD\":[{\"TM\":"
+        r"\"2025-08-28T15:02:55,000+00:00 R\",\"TX\":\"B\",\"RV\":1472.07,\"RI\":\"1-0:1.8.0\","
+        r"\"RU\":\"kWh\",\"RT\":\"AC\",\"ST\":\"G\"},{\"TM\":\"2025-08-29T12:00:00,000+00:00 R\","
+        r"\"TX\":\"T\",\"RV\":1472.29,\"RI\":\"1-0:1.8.0\",\"RU\":\"kWh\",\"RT\":\"AC\",\"ST\":"
+        r'\"G\"}]}"}'
+    )
+    with pytest.raises(ValueError, match=r"Invalid OCMF data:*"):
+        ZCONST.type_completed_session(completed_session_signed_invalid_ocmf)
+
+
 def test_update_ids_from_schema() -> None:
     """Test update_ids_from_schema."""
     ZCONST.update_ids_from_schema(set("Apollo"))