diff --git a/src/rules.c b/src/rules.c
index 7ad95c0..8dfb1b4 100644
--- a/src/rules.c
+++ b/src/rules.c
@@ -185,6 +185,11 @@ static void rules_init_class(char name, char *valid)
 static void rules_init_classes(void)
 {
 	memset(rules_classes, 0, sizeof(rules_classes));
+	static unsigned char eightbitstring[129];
+	int i;
+	for(i=0;i<=128;i++)
+		eightbitstring[i] = i+128;
+	eightbitstring[128] = 0;
 
 	rules_init_class('?', "?");
 	rules_init_class('v', "aeiouAEIOU");
@@ -197,6 +202,7 @@ static void rules_init_classes(void)
 	rules_init_class('d', CHARS_DIGITS);
 	rules_init_class('a', CHARS_LOWER CHARS_UPPER);
 	rules_init_class('x', CHARS_LOWER CHARS_UPPER CHARS_DIGITS);
+	rules_init_class('b', &eightbitstring);
 	rules_init_class('Z', "");
 }