diff --git a/sys/compat/linuxkpi/common/include/linux/mod_devicetable.h b/sys/compat/linuxkpi/common/include/linux/mod_devicetable.h
index 5becc12ef96..87bd6ec24bc 100644
--- a/sys/compat/linuxkpi/common/include/linux/mod_devicetable.h
+++ b/sys/compat/linuxkpi/common/include/linux/mod_devicetable.h
@@ -78,4 +78,6 @@ struct dmi_system_id {
 #define	I2C_NAME_SIZE		20
 #define	I2C_MODULE_PREFIX	"i2c:"
 
+#define	ACPI_ID_LEN		16
+
 #endif	/* __LINUXKPI_LINUX_MOD_DEVICETABLE_H__ */