diff --git a/lib/cmdline.c b/lib/cmdline.c
index ca89846..9e18623 100644
--- a/lib/cmdline.c
+++ b/lib/cmdline.c
@@ -35,11 +35,14 @@ static int get_range(char **str, int *pint, int n)
 /**
  *	get_option - Parse integer from an option string
  *	@str: option string
- *	@pint: (output) integer value parsed from @str
+ *	@pint: (optional output) integer value parsed from @str
  *
  *	Read an int from an option string; if available accept a subsequent
  *	comma as well.
  *
+ *	When @pint is NULL the function can be used as a validator of
+ *	the current option in the string.
+ *
  *	Return values:
  *	0 - no int in string
  *	1 - int found, no subsequent comma
@@ -53,13 +56,16 @@ static int get_range(char **str, int *pint, int n)
 int get_option(char **str, int *pint)
 {
 	char *cur = *str;
+	int value;
 
 	if (!cur || !(*cur))
 		return 0;
 	if (*cur == '-')
-		*pint = -simple_strtoull(++cur, str, 0);
+		value = -simple_strtoull(++cur, str, 0);
 	else
-		*pint = simple_strtoull(cur, str, 0);
+		value = simple_strtoull(cur, str, 0);
+	if (pint)
+		*pint = value;
 	if (cur == *str)
 		return 0;
 	if (**str == ',') {