diff --git a/drivers/misc/ibmasm/lowlevel.c b/drivers/misc/ibmasm/lowlevel.c
index 5319ea261c05..f2a110743275 100644
--- a/drivers/misc/ibmasm/lowlevel.c
+++ b/drivers/misc/ibmasm/lowlevel.c
@@ -33,17 +33,21 @@ static struct i2o_header header = I2O_HEADER_TEMPLATE;
 int ibmasm_send_i2o_message(struct service_processor *sp)
 {
 	u32 mfa;
-	unsigned int command_size;
+	size_t command_size;
 	struct i2o_message *message;
 	struct command *command = sp->current_command;
 
+	command_size = get_dot_command_size(command->buffer);
+	if (command_size > command->buffer_size)
+		return 1;
+	if (command_size > I2O_COMMAND_SIZE)
+		command_size = I2O_COMMAND_SIZE;
+
 	mfa = get_mfa_inbound(sp->base_address);
 	if (!mfa)
 		return 1;
 
-	command_size = get_dot_command_size(command->buffer);
-	header.message_size = outgoing_message_size(command_size);
-
+	header.message_size = outgoing_message_size((unsigned int)command_size);
 	message = get_i2o_message(sp->base_address, mfa);
 
 	memcpy_toio(&message->header, &header, sizeof(struct i2o_header));