diff --git a/grub-core/lib/crypto.c b/grub-core/lib/crypto.c
index 010e550..683a8aa 100644
--- a/grub-core/lib/crypto.c
+++ b/grub-core/lib/crypto.c
@@ -470,7 +470,8 @@ grub_password_get (char buf[], unsigned buf_size)
 
       if (key == '\b')
 	{
-	  cur_len--;
+	  if (cur_len)
+	    cur_len--;
 	  continue;
 	}
 
diff --git a/grub-core/normal/auth.c b/grub-core/normal/auth.c
index c6bd96e..8615c48 100644
--- a/grub-core/normal/auth.c
+++ b/grub-core/normal/auth.c
@@ -174,8 +174,11 @@ grub_username_get (char buf[], unsigned buf_size)
 
       if (key == '\b')
 	{
-	  cur_len--;
-	  grub_printf ("\b");
+	  if (cur_len)
+	    {
+	      cur_len--;
+	      grub_printf ("\b");
+	    }
 	  continue;
 	}