diff --git a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli/Commands/WriteCommand.cs b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli/Commands/WriteCommand.cs
index 507daf5..a605bf3 100644
--- a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli/Commands/WriteCommand.cs
+++ b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli/Commands/WriteCommand.cs
@@ -60,6 +60,16 @@ public sealed class WriteCommand : ModbusCommandBase
             throw new CliFx.Exceptions.CommandException(
                 $"Region '{Region}' is read-only in the Modbus spec; writes require Coils or HoldingRegisters.");
 
+        // Driver.Modbus.Cli-002: coils are single-bit outputs — only Bool makes sense. A
+        // non-boolean type (e.g. --region Coils --type UInt16) would silently coerce the value
+        // to a boolean via Convert.ToBoolean, landing as ON for any non-zero value, with no
+        // diagnostic. Reject it early so the operator sees a clear error rather than a silent
+        // type-mismatch coerce.
+        if (Region == ModbusRegion.Coils && DataType != ModbusDataType.Bool)
+            throw new CliFx.Exceptions.CommandException(
+                $"Region 'Coils' only supports boolean values (--type Bool). " +
+                $"Type '{DataType}' cannot represent a single-bit coil write.");
+
         var tagName = ReadCommand.SynthesiseTagName(Region, Address, DataType);
         var tag = new ModbusTagDefinition(
             Name: tagName,