diff --git a/pam_yubico.c b/pam_yubico.c
index 466151d..523a02e 100644
--- a/pam_yubico.c
+++ b/pam_yubico.c
@@ -404,7 +404,7 @@ parse_cfg (int flags, int argc, const char **argv, struct cfg *cfg)
 	cfg->user_attr = (char *) argv[i] + 10;
       if (strncmp (argv[i], "yubi_attr=", 10) == 0)
 	cfg->yubi_attr = (char *) argv[i] + 10;
-      if (strncmp (argv[i], "token_id_length=", 17) == 0)
+      if (strncmp (argv[i], "token_id_length=", 16) == 0)
 	sscanf (argv[i], "token_id_length=%d", &cfg->token_id_length);
     }