diff --git a/pam_usb/src/pam.c b/pam_usb/src/pam.c
index 943ba40..9ce2dc1 100644
--- a/pam_usb/src/pam.c
+++ b/pam_usb/src/pam.c
@@ -69,7 +69,7 @@ int			pam_sm_authenticate(pam_handle_t *pamh, int flags,
 
   if (pam_get_item(pamh, PAM_TTY, (const void **)&tty) == PAM_SUCCESS)
     {
-      if (!strcmp(tty, "ssh"))
+      if (tty && !strcmp(tty, "ssh"))
 	{
 	  log_debug("SSH Authentication, aborting.\n");
 	  return (0);