diff --git a/custom_components/solax_modbus/plugin_growatt.py b/custom_components/solax_modbus/plugin_growatt.py
index 2b227a12..21278232 100644
--- a/custom_components/solax_modbus/plugin_growatt.py
+++ b/custom_components/solax_modbus/plugin_growatt.py
@@ -64,7 +64,7 @@ async def async_read_serialnr(hub, address):
         inverter_data = await hub.async_read_holding_registers(unit=hub._modbus_addr, address=address, count=5)
         if not inverter_data.isError():
             decoder = BinaryPayloadDecoder.fromRegisters(inverter_data.registers, byteorder=Endian.BIG)
-            res = decoder.decode_string(12).decode("ascii")
+            res = decoder.decode_string(10).decode("ascii")
             hub.seriesnumber = res
     except Exception as ex: _LOGGER.warning(f"{hub.name}: attempt to read firmware failed at 0x{address:x}", exc_info=True)
     if not res: _LOGGER.warning(f"{hub.name}: reading firmware number from address 0x{address:x} failed; other address may succeed")