diff --git a/grub-core/lib/division.c b/grub-core/lib/division.c
index 920a79f18..35606fea7 100644
--- a/grub-core/lib/division.c
+++ b/grub-core/lib/division.c
@@ -50,7 +50,8 @@ grub_divmod64s (grub_int64_t n,
       q = -q;
     }
   /* Now: n = d * q + r  */
-  *ro = r;
+  if (ro)
+    *ro = r;
   return q;
 }