Add const to suppress compiler warning
diff --git a/auth-pam.h b/auth-pam.h
index 1f3bc25..191d80c 100644
--- a/auth-pam.h
+++ b/auth-pam.h
@@ -8,7 +8,7 @@
 int auth_pam_password(struct passwd *pw, const char *password);
 char **fetch_pam_environment(void);
 int do_pam_account(char *username, char *remote_user);
-void do_pam_session(char *username, char *ttyname);
+void do_pam_session(char *username, const char *ttyname);
 void do_pam_setcred();
 void print_pam_messages(void);