diff --git a/kern/crypto.c b/kern/crypto.c
index 83e2d96df..d097e1668 100644
--- a/kern/crypto.c
+++ b/kern/crypto.c
@@ -30,7 +30,6 @@ grub_burn_stack (grub_size_t size)
   char buf[64];
 
   grub_memset (buf, 0, sizeof (buf));
-  size -= sizeof (buf);
-  if (size > 0)
-    grub_burn_stack (size);
+  if (size > sizeof (buf))
+    grub_burn_stack (size - sizeof (buf));
 }