diff --git a/tools/power/acpi/common/getopt.c b/tools/power/acpi/common/getopt.c
index 24966290ad1c..efefe309367a 100644
--- a/tools/power/acpi/common/getopt.c
+++ b/tools/power/acpi/common/getopt.c
@@ -47,6 +47,7 @@
  * Option strings:
  *    "f"       - Option has no arguments
  *    "f:"      - Option requires an argument
+ *    "f+"      - Option has an optional argument
  *    "f^"      - Option has optional single-char sub-options
  *    "f|"      - Option has required single-char sub-options
  */