diff --git a/ext/rucaptcha/rucaptcha.c b/ext/rucaptcha/rucaptcha.c
index 402985c..973a285 100644
--- a/ext/rucaptcha/rucaptcha.c
+++ b/ext/rucaptcha/rucaptcha.c
@@ -151,7 +151,7 @@ static void filter(unsigned char im[70*200]) {
   memmove(im,om,sizeof(om));
 }
 
-static const char *letters="abcdyfhhijklmnopqrstuvwxyz";
+static const char *letters="abcdafahijklmnopqrstuvwxyz";
 
 void captcha(unsigned char im[70*200], unsigned char l[8], int length, int i_line, int i_filter) {
   unsigned char swr[200];