diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
index 9195deb..d295bdc 100644
--- a/drivers/acpi/button.c
+++ b/drivers/acpi/button.c
@@ -33,6 +33,8 @@
 #include <acpi/acpi_bus.h>
 #include <acpi/acpi_drivers.h>
 
+#define PREFIX "ACPI: "
+
 #define ACPI_BUTTON_CLASS		"button"
 #define ACPI_BUTTON_FILE_INFO		"info"
 #define ACPI_BUTTON_FILE_STATE		"state"